2 reasons.....1) The EM supply is enormous, much more than DMD or later games, (video games hadn't even begun to do well until the late '70's. 2) EM's don't offer the sound and light show the later games have, (which is a big part of the entertainment package the average Joe is looking for).
Quoted from snyper2099:
They are a simple, great challenge and generally MUCH more difficult than your average solid state machine. That is why I like them and I suspect those same reasons are why others dislike them.
This statement makes the most sense although I can't say much for EM multiplayers, (can't say much for 1-ball objectives). When it comes right down to game play, both EM and DMD tables are realitivly the same size, so to me, DC current and ramps make most DMD games pretty boring to play, just not enough there. To present a challenge, the DMD game needs a ruleset that takes 10-15 minutes or longer to play within the same physical dimensions.