I was looking the other day some NES clone footage, and I was surprised to find out that there is a ton of them. I am wondering, how could they be so many since Nintendo did not use standard off the self components? (As far as I know, the NES utilizes a custom 6502 based CPU, which handles audio, too)
Per Nerdly Pleasures:
... back in the 80s and early 90s, Famiclones were typically made in Taiwan. Frequently they simply cloned the die of the official NES CPU and PPU. At some point, the Taiwanese semiconductor fab UMC made clone chips of the Nintendo/Ricoh 2A03 CPU and 2C02 PPU. They were called the UA6527 and UA6528, respectively. ... This design prevailed for the most part when these chips were reduced to the single NES-on-a-Clone (NOAC) chips of the late 1990s until the present.
So that states that after a period of simply copying the original dies, UMC offered NES clone chips as a standard commercial product and that these later shrank into a single chip.
Therefore the high number of clones is just because the chips were available off-the-shelf from a reliable mainstream source, despite Nintendo having designed them as custom parts originally.
Taiwan is to this day not a member of the Berne Convention, which has governed international recognition of copyrights since the 19th century, though it signed up for the WTO's TRIPS agreement which is a 1990s instrument that goes beyond copyright to other areas of intellectual property. So it is likely that Nintendo had no recourse against UMC during the 1980s and had stopped caring about NES clones by the N64 era.