Why is Nc3 considered so much worse the Reti?

I mean, they both develop a knight and there are plenty of positions where Nc3 is played.

It blocks the c-pawn. This pawn break is important in a number of openings (I know that even in systems like the OIA, c3 is vital)

There are more positions where c3 or c4 is played than positions where f3 or f4 is played. For example, 1. Nc3 d5 2. d4 immediately reaches a position where c4 would have been a better move than Nc3. There's 2. e4 of course, but it's not like it's considered that good either (and if the best white could get after 1. Nf3 e5 was 2. d4 e4 then 1. Nf3 would be considered pretty bad as well).

While 1. Nf3 does give up the option of playing f3-based setups against, say, the KID, white can still transpose into many 1. d4 main lines or into the English.

Nc3 is BEST opening

1 Nf3 stops 1...e5 and prepares O-O. 1 Nc3 does not stop 1...d5 and does not prepare O-O.

I have never heard 1. Nc3 is worse. But you can certainly say it's a lot less popular.

1.Nf3 is a very flexible opening (you can transpose into 1.d4, 1.c4 and sometimes even 1.b3 and 1.e4 openings, depending on what you feel like). Or if you don't like any of those, you can play g3 and do a Kings Indian attack. 1.Nf3 controls the center and doesn't weaken your kingside. Pretty much the only downside of 1.Nf3 is it stops you from screwing around with f3, f4. Did I say downside?

1.Nc3 on the other hand is not so flexible or good. You can't transpose into 1.c4 openings because you've just blocked your c pawn. You can still play d4, but you'll just get inferior versions of d4 openings (eg. 1. Nc3 d5 2. d4, and your c pawn is crying because it can't strike at d5). So a lot of 1.Nc3 players try for e4 systems instead. Sometimes it works (1. Nc3 c5 2. e4 is the closed sicilian, 1. Nc3 e5 2. e4 is the Vienna, neither of which are so bad), but e4 is hard to play when black plays d5 (eg. 1. Nc3 d5 2. e4). Black can grab space with 2..d4 and white has to waste time playing Ne2 and Ng3. With correct play, black can claim advantage.

These reasons are why 1.Nf3 is considered to be theory, and 1.Nc3 just a prank opening for people who want to play different. It's not like 1.Nc3 is losing or anything, but there are much better openings.

@blind_man_walking

No this is incorrect. You're interpreting it as if "it IS worse because.." . There are plenty of new wave theory that top players are playing where Nc3 is an active part in playing. One in particular has been gaining popularity because of recent games by GM Jobava being a practitioner of Nc3 theory.

So.. I guess the question is. If GM Jobava who is a 2700+ GM can't be proven worse against other GM's, why do you think you can prove him wrong?

Not everything has to be a glorious matter of playing c4. There are plenty of systems that have e4 and f4, or even d4, e4, f4 without ever playing c4.

Last, I don't even remotly agree that 1. Nc3 d5 2. e4 gets black an advantage. Especially considering the only line you consider is Ne2 and Ng3. And that you think after 1. Nc3 d5 that 2. e4 is the only way to fight for and advantage or equality. One example is the Two Knights French which is basically a possible theoretical transposition into your line.

1. e4 e6 2. Nc3 d5 3. Nf3 d4 4. Ne2 c5 5. c3 <--- at this point white can claim slight advantage. And even having white set a trap for black which a lot of people have fallen into.

What you are stating is an opinion. Not theory..

Yes objectively 1 Nc3 and 1 Nf3 are equivalent in a sense that they most probably both lead to a draw with perfect play from both sides.
1 Nc3 is played at top level

However 1 Nc3 d5 2 d4 transposes to 1 d4 d5 Nc3 which is considered passive for white.
1 Nc3 d5 2 e4 transposes to 1 e4 d5 2 Nc3 which is considered not as strong as 2 exd5.
After 1 Nc3 d5 2 e4 dxe4 3 Nxe4, black can transpose to Caro-Kann with 3...c6, to French with 3...e6, but he can also play 3...e5.

I think nc3 is a bad move usually in openings except scandinavian and hungarian defence c pawn of white is not blocked and by nc3 it gives some passive position to white or two tempos to black.
c3 or c4 is usually compulsory in white to do list
like c3 in alapin or french
and c4 in queens gambit