You can still buy them from WDC, part #W65C02S: https://www.mouser.com/ProductDetail/Western-Design-Center-W...
I guess for these type of products, where the wafers is not what costs (the 6502 is ~3.5k transistors), but overheads of dealing with small runs and packaging or investing in upgrades...
Anyone looking for large quantities of 6502-compatible cores presumably are mostly licensing cores to embed into something else.
But of course even a PLCC-44 package is big compared to that die.
[1] https://eu.mouser.com/ProductDetail/Western-Design-Center-WD...