@nazokiyoubinbou @mcjonestech
This was still in the era where you'd typically buy a IBM 5150 or a Seequa Chameleon through a local dealer. Your dealer would be happy to put an 8087 in there for you so you had it day one.
When you pick up an old PC, XT, AT, you'll often find the original dealer's business card or placard or badge attached to the system somewhere.
PC makers were furiously competing on price, so you'd never want to pad out the price of your lowest-cost model, which is gonna be printed in the largest font to catch your eye.
The 8087 was an incredibly complicated chip for the time and fairly expensive when it came out, like several hundred dollars expensive, and not a lot of software actually needed it. Floating-point could be done in software, and was - even in ROM BASIC.
So, at least at first, you only bought an 8087 if you needed floating point to be fast.
I think the longer you held on to your IBM PC the likelier it would be to at some point get an FPU in it, as you tried to trick it out to extend its lifespan. By 1987 they had dropped to $100.
Both of the 5150s I currently own came with 8087's installed, and at least one of them I know was from the original owner. They are not particularly rare, but I could only speculate on the total adoption rate.