Chess (orthodox chess or 'FIDE') is very hard to master and a very
difficult game to compete in. The real reason most give up on chess is
because there is too much competition and to get an 'edge' one must be
sufficiently knowledgeable in opening theory (but not excessively
memorizing lines as this does NOT improve play), constantly analyze past
games with the help of a computer and also analyze high level games
played. Not to mention constant practice.
Online resources are normally filled with players playing in realtime
especially 2/12 5/12 blitz.
Any chess variant with same rules but with extra pieces with sufficient
popularity will reach this stage (though larger board games it would be
difficult for humans to memorize as much lines).
Computers aid most modern chess players in analyzing games and do not
contribute to any 'decline' in chess except in the eyes of spectators
not too familiar with chess who may not respect the chess player for been
beaten by a computer.
Computer programming has advanced sufficiently that a program can be
written for any game that relies on perfect information.
Computers are only behind in games with psychological aspects such as
poker.
The effect of computers on chess popularity - None, except to serve as a
useful learning tool.