1. The format. Whereas the CD was mostly a benefit for PS1 (minus load times and scratches), UMD was an anchor for PSP. DS wasn't really trying to compete with PSP in specs like N64 was with PS1, so the much smaller storage space of the DS Game Cards isn't a big deal like it was on N64. Sony realized this eventually and released PSP Go as well as using Game Cards for PS Vita. Optical drives on a handheld are not a good idea.
2. PlayStation is simply better at making home consoles than handhelds. Just because they kicked Nintendo's butt with PS1 (and especially PS2) doesn't mean that will translate to portable consoles.
3. DS had first-party games that lit the world on fire. Nintendogs, Pokemon, Mario, etc. Also, in terms of the library DS and DS Lite can play GBA games.
Lifetime Sales Predictions
Switch: 161 million (was 73 million, then 96 million, then 113 million, then 125 million, then 144 million, then 151 million, then 156 million)
PS5: 115 million (was 105 million) Xbox Series S/X: 48 million (was 60 million, then 67 million, then 57 million)
PS4: 120 mil (was 100 then 130 million, then 122 million) Xbox One: 51 mil (was 50 then 55 mil)
3DS: 75.5 mil (was 73, then 77 million)
"Let go your earthly tether, enter the void, empty and become wind." - Guru Laghima
