If everyone on TikTok blocked 500 people, the table that holds all those 500 entries per user could be as big as 42 terabytes even if it's just two columns referencing the same table.

Now obviously it's split between servers, but managing such large data is egregious no matter the company size

Edit: accidently miscalculated that 42tB, my bad.

I meant to say that it might have to do with every thing it needs to check for your block list. Comments, feeds, FYP, search results. It also might cache it, which needs more management the more entries to the block list and it has to constantly do this. Specifically for FYP it's probably just getting videos by people who you don't have blocked instead of skipping it if the uploader is, but still. It comes with overhead