if you want a real answer, here it is:
1) not everyone has a DVD-ROM. believe it or not, most OEM computers in the high end have been shipping with DVD drives for some time. i'm pretty sure that trend hs trickled down to the midrange and lowend by now. last year two friends built themselves computers and did NOT buy DVD drives. they later replaced their cd-rom drives with DVD drives. most people with vintage computers TNT2/V3 era almost certainly did not come with DVDs. developers are still making games that support these cards
2) expense. 2 CDs are much cheaper than 1 DVD. you can buy 100 cds for the price of one DVD-R(W?). cds cost nothing to produce, DVDs do.
3) need. we hardly need to use DVDs when most games are still only using 1-2 CDs.
4) until DVD-RW drives become more popular, and every computer has a DVD drive, don't hold your breath for DVD games. it would help if the medium were mass produced more too