If you kill a wizard, they drop a spell book. If you befriend a wizard, they can teach you spells.
Wizards having all the spells they want in their book is included in their class balance equation. That’s why scribing spells more cheaply is a subclass feature. If you block the wizard from access to spells to copy you are removing a class and subclass feature. That’s clearly a nerf.
I suspect a lot of DMs and pkayers dont psy much attention to it.
Probably mostly there for the rare occasions soellvooks or whatever turn up.
Theres very few actual wizards left in the MM. I think theres 3 being generous.
Treasures funny in 5E adventures. Some adventures flood you with it others youre broke. Sometimes theres nothing to spend it on as thry just what available from the vendors. If there is a vendor.
Ive ran 2 adventures. Lost Library gave out around 800-1000 gp iirc.
A Deep and Creeping Darkness not sure. Neither had a vendor. I added one to PC home base. Knowledge cleric is doing the ritual stuff as such.
Haven't gone through my 2024 starter set or all the loot in Adventures of Faerun book.
If youre not used to forum chat it may not be obvious that you could maybe want to buy that stuff.
Its a very big assumption you can buy whatever you want in the quantities you want, wherever you like and the DM has provided the funds.
If the money was split evenly the wizard would have 150-200gp lvl 3. Halfway to 4th maybe another 100. No vendors in the adventures (I've added a home base).