For starters, I have both CRTs and a high-end LCD in my house, so don't think I'm an LCD hater... having said that, to answer your question:
#1: the VAST majority of the computer market uses CRTs, not LCDs.
#2: it costs EXTRA money to make all those DVI->VGA converters
#3: of the minority who do have LCDs, you have an even SMALLER fraction of an already small number who have DUAL LCDs (the ONLY people who need dual-DVI).
#4: Mabye CRT users don't want extra-long, accident-waiting-to-happen extensions sticking out the back of their case because they're forced to use DVI->VGA converters by the .03% of the computer market who use dual LCD monitors.
#5: LCDs will NEVER become the defacto monitor as CRTs have been and still are. Newer, better technologies will replace LCDs soon, including newer, better, thinner, cheaper CRT screens and some of the other new display technologies coming out.
Frankly, I'm surprised there are as many dual-DVI cards as there are on the market... if anything, there should be fewer!