Alpha 3 was competitive from 1998-2002 (it was featured in some majors after that, but usually as side tournaments). Valle was the first Alpha 3 champion, but was later overtaken by John Choi (I think by Mike Watson, too). East Coast guys like Eddie Lee, Arturo Sanchez, Jeron Grayson were also great. The Japanese were on another level late in Alpha 3’s span.
There isn’t one factor why Alpha 3 isn’t played anymore. IMO, the reasons are:
-Lack of a console port (before 2006), when EVO and other majors started moving to console in 2004, this put an already faded Alpha 3 on the back burner. There was no good port for the game, DC and PSX versions weren’t true to the arcade, Saturn was the closest, but was very hard to find and wasn’t quite arcade perfect.
-Newer games coming out. CvS1, CvS2, MvC2, TTT, T4, SC2, GGXX, etc… were out and with the old saying, “out with the old, in with the new.” It is very hard to run so many games in one tournament, unless the number of entrants for the games are very low.
-People didn’t like how the game developed. Pretty much, other than a few characters (Guy, Bison, Gen, maybe Dhalsim, though he can use all the ISMs will), if you aren’t using V-ISM, you’re screwed. Crouch Cancels were found out, and many people didn’t like it. IMO, crouch cancels make Alpha 3 one of the most balanced fighters, but people don’t like seeing someone get juggled in the air for 90 seconds.
Alpha 3 isn’t like other SF games, it plays like one, but… Kyokuji put it best: Alpha 3 is like a meter cold war, meter first, the SF second. It is the most technical SF game (I believe that MvC2 is more technical, possibly CvS2, but those don’t have SF in the title). The game feels weird, due to the wonky hitboxes, and as I mentioned before, if you aren’t using V-ISM against a decent opponent, then you’re in for a rude awakening. The game is a bitter pill to swallow, and while I like the game a lot, I can understand why many others (even good players) don’t, which is why I don’t think I can consider it a great game.