Google decided to delay the release until apple updated their unknown tracker alert to support google's bluetooth tracking devices. Not sure why, but it took one year for apple to implement the support.
That still leaves 2 years past Apple’s long rumored debut.
Presumably Google would have, eventually, said "ok, enough is enough, we're releasing on X date whether or not you've updated yet". And maybe that's indeed what happened! At that point Apple really would want to finish that update, since not doing so could be a privacy hole for their customers. (The same privacy hole Android users had to deal with in the early days of AirTags when we couldn't detect them.)