Why do I still suck at Blitz?

I consider 2100 on lichess bad because my FIDE rating is above 2000 and in the past year I finished 50% of my tournaments with a performance at or above 2100 and my rating is steadily increasing.
What I mean is, that people with a comparable OTB strength are better at online blitz than I am and I'm looking for ways to change that!

@dRr0x0rZZ
We should play against each other, since we both suck at blitz. At least one thing in common.

@breakreign
Your theory is easily refuted if you look at times when I had a really bad day (maybe was in a rage) and dropped below 2000. I got up by myself easily, playing lower rated opponents than I usually do.

"Playing against the 1.9K + rated people he constantly plays against he only gets to see a handful of play styles; not being surprised and instead of having to use thought and critical thinking; he uses memorization and repetition. "

This is nothing personal, but I really urge you to reconsider your view on chess mastery/strength. The fact that you argue like this shows that you haven't really understood what it actually means. It means being significantly better than others at at least some of the following:
positional play, calculation (most likely), endgame knowledge, theory knowledge, endgame technique, resourcefulness etc. Bad moves stay bad moves. There is no such thing as a surprise factor.

I'll tell you a couple reasons why I don't like facing much lower rated opponents:
1. Most of them know that their best chance lies in winning on time against a stronger opponent. I'm always at a general baseline risk of losing a certain percentage of games on time. Thus, if I play against weaker opponents, I not only play games of poorer quality, but also lose a similar amount of games on time, regardless of my position.
2. I hardly learn anything from playing much weaker opponents
3. Because it is easier to use being a good time player to your advantage at a lower level, I might even play against somebody rated at 1500 FIDE or below (they can get to 1800 lichess).
4. I prefer a challenge to having the upper hand
5. I still have ambitions to improve

2100 isn't "sucking at blitz" it's better than 97% of people.

Anyways just practice more, and study your games, and games of Masters, and listen to GM lectures, and do puzzles, and keep working at it.

@hatchet #1
Personally I play blitz for fun, for entertainment, and to try new ideas. I try not to focus too much on blitz rating. However when my blitz rating goes under 2000 I kind of start to wonder why this happens, and there can be all kind of reasons.
* Playing too much in a row
* Bad luck with openings against certain opponents
* Not feeling very well or just tired
* Playing too aggressive in the opening and middlegame
Long time ago I set myself a goal to go over 2300 blitz rating on Lichess. I did put a note with a big "2300" on it next to my computer, a note which I would see every day, and I did manage to go over 2300 during a Lichess Marathon, and winning against a GM in that Marathon as well.
Marathons turn out to be interesting to gain rating points, because there is much more chance to end up getting paired against (possibly "tired") 2300+ players.
But lately, while not doing that well in real life as before, I see that my blitz rating goes up and down 1900 to 2150.
What I try to focus more on now is to explore better which openings would suit me well. Looking at the amounts of mistakes I make and the ACPL in analysed blitz games, I found out that several openings gave me too many games with too many mistakes or with disadvantage in the openings.
For example, as black, both Caro-Kann and Nimzo-Indian give me games where I make far less mistakes than for example Benoni structures and Sicilian.
Of course I could work on those openings, but I still need to work on my current opening choice, and there is also non chess to do.

I suck in chess in general, not only blitz :))

My rating figures might look ok, but seeing the time i devoted to chess....kids aged 10 or so become FM, i'm far away from that despite all the effort...

@hatchet, i believe blitz has a "real chess" and a "gambling" component: one needs both! Maybe the latter is underdeveloped?
(I'm often "reverse", lacking good moves but getting a practical edge due to beeing very fast - "gambling". It's improving practical results, but not improving one's game...)

@hatchet, i quickly browsed through 10+ randomly chosen games of you. Just my 2 cents...

Saw a lot of good points; feeling for position types and "what to do" is often ok, tactics ok, endgame is ok.
Dont know your tournament games of course, but i see at least 2 practical issues regarding blitz:
1) time management: sometimes spending simply too much time on not too important moves. Example:

Moves 23+24 take you 1:15 with 36 secs remaining (and the moves were rather bad in this case). Dont spent so much time here - it's not a killer combination, youre not facing immediate defeat - save time for later when needed.
(True, white ideally should find some kind of plan here, but accepting two new burdens with "no time left" and stripped king can't be the way. Sometimes better do "nothing", just improve slowly or defend and see what happens...)
2) Rather broad "main line opening repertoire" lacking deeper knowledge. Esp. in some 1. e4 games with you as white i saw you running into variations your counterpart obviously knew better. I feel this is really one main disadvantage of 1.e4 - black can throw all kind of stuff at you, sometimes not reasonable according to book, but reasonable enough...and the blacks invariably know their stuff!
Another issue - sometimes "bad mood" collapses? Several quick losses in a row, no fighting spirit? Just rest, if only for 10 minutes...

So, in one sentence: mostly proper chess (really like the way you play), but some practical issues.