Quoted from TheLaw:
Because they don't play as well, and have just the worst art ever. Newman's fingers in the first pic for reference.
I don't think that DE games play any worse, I think that it is a hang over of the ops opinions of them from back in the day, much like a lot of the stuff in our hobby is still ultimately based on ops from the 90s... (and indirectly, players in the 90s actions)
DE games were known for making good coin but not being very reliable. From what I was told, they made the best coin for a while, but had a bunch of issues during that time. JP is a perfect example of it - the code was updated for the T-Rex movement a whole bunch, there were service bulletins for the A-hole's switch diode, and because of this JP might be out there earning great but costing the op five service calls a week.
B/W games needed to be dialed in, but then generally held up well and earned solidly.
Gottlieb games were built like tanks, but earned the least of the three manufacturers.
Because of this, ops were more willing to sell DE games cheaper back in the day, and people remember the DE titles less than the big B/W games that lasted on route for years because of it. I know of a bunch of B/W games still on route, but basically no DE titles. the perception was that the DE games weren't as good, and that lingers.
The only thing that does drive me nuts about DE games is that their modes are ridiculously similar. I had JP and Tommy side by side for a while, and although they are both great games, it started driving me nuts how similar Tommy played, so I swapped it out for a different game. It seems like almost all DE DMD games are like that - JP, Tommy, TFTC and WWFRR, all games that I own, all with wildly different playfields, all have rather similar rules. In a smaller collection, I wouldn't need all four - I'd pick my favorite playfield and keep it around.
Contrary to popular belief, I don't feel that the DE games play any more "clunky" then anything else - for that trophy, play my JD or Popeye - and I've had far more problems maintaining my B/W titles then my DE ones so far, but I chalk that up to luck, not anything to do with the manufacturer.
Oh, and DE pops suck, I've detailed before that you should swap the spoons out to Williams ones as that does make them about fifty times more responsive. That is the one design thing that I do think holds them back. That, and the fuse clips, but that's a pretty small deal.