The Google backing. See ublock Origin for example. Google wants less effective ad blockers because ads are 90% of their business. Google removed manifest v2, which is needed for good ad blocking capabilities. Now Chromium, and any browser based on it (Edge, Brave, Vivaldi, etc.), also lose it. Some have said they will manually add it back in to their browser, but that will only be possible for so long as Google’s upstream Chromium base further diverges.
The massive market share of Chromium-based browsers also gives Google near complete control over web standards. There are many websites that use non-standard functionality that only works in Chromium and not Firefox or Safari. Developers also will not adopt new standards unless Google chooses to as well because there would not be enough users to justify it otherwise.
TLDR: Control over Chromium gives Google extremely strong influence over the web and their interests likely do not have much overlap with yours.
I used Thunder for a long time, but I have been giving Arctic a try lately and like it. I will likely give Mlem another shot after the next update. Voyager is another great one, but I have not used it for a while.
Overall, there are a lot of great Lemmy apps and I love that most of them did not get abandoned after the initial wave from the Reddit exodus died down. I think we have more high-quality Lemmy apps than there were for Reddit.