Because it's not a choice of FOSS or not, it's a in choice of quality of the app. Apps like Jerboa or Thunder are very far behind Sync and Boost. But if you enjoy those, then more power to you, and definitely no reason to switch.
I don't know about that. I'm a sync user and some of the foss options are very good by now. I use sync because of familiarity and I like the dev so don't mind dropping some money to support him.
Also a Sync user, for me the only option that came close to Sync and Boost for me was Summit, which people also did not like due to it being closed source.
Thunder is kinda close, as is Connect, but AFAIK Sync is still the only one to have any admin tools built into it (haven't been able to try out Boost for Lemmy yet).
I was just more amused that it was an Adblock ad. It's a pity it is relying on hassling you with ads to get you to pay as I'd happily chip if to help with the development of an app I was enjoying.
Adception - how deep does it go? Do other ad-blockers advertise in AdBlock's site? Do they pay for ads to be alongside other ads for ad-blockers saying "want to stop ads like those guys? Then use us". What if, ultimately, the only ads are for ad-blockers?