Given enough eyeballs, all bugs are shallow
Of course, more eyes on the code will help you find and fix more bugs, but you must not fool yourself into believing that just because you have a huge user base this automatically means that a lot of people have actually read the code. Few users ever read the code of any project. Including popular ones.
People rather follow each other, meaning the network effect of "they use that product so then I shall as well" is explaining usage much more than the absence of bugs. An old and well-used project is expected to have been vetted and scrutinized already by someone else.
This said, rarely used and unpopular projects probably are reviewed and scrutinized even less. If 0.2% of users read a piece of the code, at least more users make a few more readers.
All bugs could in theory eventually be found. But only if you stop adding new features and you have a large amount of users for an extended period of time.