The ultimate reason is that not enough people are going to schedule hours out of their day to play a single game online which may or may not end with your opponent quitting halfway through, or which leaves you open to engine abuse.
More specifically, the problem is that a classical game of chess takes hours, and that means that if two people want to play, then they each have to believe that the other party is just as committed as they are. In-person, this is easy: you've both shown up, you say hello, maybe you already know each other, there's good reason to expect a post-mortem discussion afterwards, maybe there'll even be time to go for drinks. Online, it's nothing like that: you get "paired" with a random stranger, probably they aren't talkative, you have no idea what they're doing on the other end, you can't tell when/if they're at the board, and since you aren't both in the same location there is no feeling that you've both decided to stay until the end of the game.
I could spend an hour playing a horrible game like that, or I could spend an hour playing 6 games of blitz, which doesn't suffer from any of those problems. Which do you think I'm going to choose?
(Which one is better for my chess is a different, irrelevant question.)
@biscuitfiend I agree with you although I have to say that this mentality reminds me of:
"I can't have my favourite beverage, I don't know how this stuff will taste here, so I'll go with just water before risking to get dissapointed"
"I can't have this one girl or I don't know how the relationship will go with this one so I'd rather just stay alone the rest of my life before risking to get hurt"
It's a pessimistic mentality leading only to loss and never to joy
@WinOr10PushUps I see your point, it does sound like that. But I disagree with your conclusion. I enjoy playing blitz. I'm not saying "I don't know how my favourite stuff will taste here, so I'll just have water". I'm saying, "I know for a fact (I've seen him do it!) that the barkeep here waters-down my favourite drink (to save on costs or whatever), so I'll go with my second or third favourite drink instead. Once the place across the street opens up again (post-pandemic difficulties), I'll be able to have my favourite drink again, and I can live until then."
@biscuitfiend Word. ^^ I can't wait myself for the pandemic to end. I am stuck at 4 rated games and I get my first ELO rating after the 5th *sigh-facepalm* never got to play that xD
And I really felt that when you said going on a drink afterwards and analysing together. That was exactly what I always did.
I for myself really enjoy classical on lichess too.
Only a handful have the Patience to play classical. I"m not young but I won't sit play classical online or otb. I will play 15/10. That's as far I get. And occasionally only.
I prefer classical myself. Online however, if somebody wants to say, run the clock out or other unsporting activity, Rapid is less time wasted, just stick on a tune and sit it out. Against my computer chess set I only play classical and at a setting where by I never ever win. When I beat that setting I will know I am getting somewhere but I shall not hold my breathe.
Hopefully here (in the UK), social distancing might end in June and clubs can start again, I had only just joined one about 6 weeks before all this covid stuff kicked off. I borrowed a book off one of the other members and it is well overdue its return!