Because the Boyd Family gifted all that land to UNLV. We always sucked at football so there was little justification to build a stadium elsewhere.
Plus in the 80s the casino business changed from family owned/run industry by people who lived in Las Vegas to the corporate run industry with publicly traded stockholders and CEOs who couldn’t care less if UNLV is successful. The money needed to secure a loan or huge donations was now corporate dollars. Mix in a board of higher education that used to be run by a majority of Northern Nevadans/UNR grads and you have a disaster for UNLV. It’s slowly changed and it’s much more favorable for UNLV.
If not for the Raiders we’d still be playing in that dirt lot.