Not sure what the technical challenge here is either. I use an ad blocker and I assumed YouTube already counted my view, since the video can be found in my YouTube history.

I imagine watch history view tracking and view count view tracking and possibly even ad impression view tracking are three disconnected systems. Google is still going to update your history view even if it thinks you're a bot so you don't know you're being filtered out for example. The data to power that UI can also be partitioned by user while the ad and view count data needs to be aggregated performantly across large numbers of users in different slices. On the other hand your watch history doesn't keep multiple entries if you watch the same video multiple times in a day (say a music video on loop) but does want to charge for each ad impression seperately.