Probably because v2 extensions haven't been switched off yet. It might be different in January 2023; or maybe the limited adblocking of v3 will be enough for most people. Time will tell.
Ad providers are obfuscating domains to bypass blocks. Currently only ublock origin deobfuscate and block based on the original domain.(It is supported on firefox only anyway) But after the change... I guess no one on chrome can do. And ad blocking will be totally useless at that point.
If you mean ublock origin cosmetic filters, yeah facebook is really putting up a fight. The status quo has been randomized css classes, identical html structure, interspersing hidden junk characters in between the "Sponsored" text, and the latest I've noticed, anchors that link to # until you hover over, preventing blocking href=^/ads. That and turning on or off or changing behavior between users and regions makes collaborating on rules really difficult.
This has me surprised because most of these changes are not very complicated and I have always wondered why these methods weren't more widespread. To me defeating ad blockers seems easy as long as you're willing to play cat and mouse (and if your income depends on it I guess you are)
Around which time Firefox is intending to make the same changes, having deprecated v2 manifests (this post seems to use that term to mean the actual removal) and doing all the API swaps to service workers and the such. Firefox just makes all the same decisions Chrome does, the good and the bad.
Mozilla does plan to support the old request-blocking APIs indefinitely, though, even after the Manifest v3 switch, until an alternative that meets the needs of extension developers is developed.
