Apple and Firefox brought this on by killing 3rd party cookies. The reason why client send requests to the 3rd party domain directly is that the cookies attach

Apple and Firefox brought this on by killing 3rd party cookies. The reason why client send requests to the 3rd party domain directly is that the cookies attached to that domain are sent and which can track you better! With a server-side request there's no way to use that cookie info. But browsers increasingly limit 3rd party cookies. With 3rd party cookies becoming useless for tracking there's far less to lose by moving all these analytics calls to the server side.