It's also doing CNAME uncloaking, request rewriting, stubbing functions in pages, it has syntax to handle CSS changes, it has rules that allow requests to only go through in certain contexts or if they're originating from certain domains. And most importantly, there's a giant community of people basically standardized on Ublock Origin who maintain all of these lists and who are constantly identifying new threats and proposing new features.
So a competitor to Ublock Origin would need to be constantly competing with it, it would need to be pulling in new features as they got released, and it would need to be consuming the same lists that Ublock Origin uses. It's just really hard to keep pace with that.
If Mozilla came out tomorrow and said they were going to do native adblocking, I would trust them less than Ublock Origin. I don't think even they would be able to keep pace if they were trying to build a community from scratch.