Reddit has over 1,000,000,000 active users per month. Lemmy has about 50,000. The API fiasco was a big deal for lemmy, but it was not a big deal for reddit. Lemmy is a rounding error to them.
I would also bet that a lot of lemmy users still visit reddit for their niche communities. I know I do, even though I host a server for my own niche hobby, but I’m the only one who’s ever posted anything to it.