I think you're in the minority. I can't find the reference, but I believe more customers are willing to pay $100/month for Tesla FSD than are willing to pay $10K once.
And of course there's the fact that you can turn monthly FSD off if you feel the value isn't there. The commitment is much lower, so it's easier to convince people to give it a trial run.
I don't pay for it, though. I still haven't been that impressed with it (we've gotten a couple free months to play around with it). I think in some areas it works pretty well, but in my neighborhood it makes regular attempts to scratch the car.
So even though paying monthly is more amenable, the vast majority don’t want to pay anything.
[0] https://www.businessinsider.com/tesla-full-self-driving-sale...