My guess is giving up conversion tracking is the #1 hurdle for adopting alternate privacy-friendly (aka. no conversion tracking) analytics solutions.

It means that people using a privacy-friendly conversion tracking solution literally cannot track conversions accurately. If you can't track conversions, it also means you can't run advertising campaigns effectively because so much of advertising relies on conversion tracking to know whether ad spend is having an ROI or just burning money.

Then again, perhaps the target users of a privacy friendly analytics solution aren't in the same category of people who are running paid ad campaigns on Adwords, etc.