Actually N64 games were usually much bigger than PS1 games.
Banjo-Kazooie, Banjo-Tooie, Conker and Super Mario 64 are far bigger platformers than the Crash Bandicoot trilogy.
Ocarina of Time and Majora's Mask are far bigger adventure games than anything on the PS1.
Goldeneye 007 and Perfect Dark obliterate any FPS games on the PS1.
Mario Kart 64 & Diddy Kong's Racing are around the similar size of Crash Team Racing.
Don't know about you guys but Final Fantasy VII looks like ass compared to Paper Mario visually speaking.
All that extra space on CD-ROMS went to silly looking FMVs and voice acting lol. Cringeworthy voice acting might I add. The FMVs worked wonders to convince people to buy the PS1 though, that can't be denied. Also the much cheaper option, something that also can't be denied.
"The strong do what they can and the weak suffer what they must" - Thoukydides