That way it wouldn't be possible for users to block individual hosts to prevent tracking. I guess it's not worth the effort though because laypeople won't care either way?
Some content providers don't allow you to view content if you block the advertising hosts.
Then it becomes a matter how you want to deal with failure, do you want the site to break if your ads don't load?
This. I remember at my last company, we ended up with 8 or 9 different analytics tools all getting different data and showing one or two "cool views" the PM had put together.
It's such a big problem that solutions like segment.io exist to broker your events to N different downstream solutions.
Truly, this is the darkest timeline.