I don’t think this is true. If it was true, it would be possible to help resolve these cases by contributing to the triaging of issues – pinging people on PRs that fits this criterion, for example. Would you like to provide examples of such PRs? (I’m assuming that the PRs have been reviewed – otherwise of course they cannot be merged – and do not conflict with evolutions in the codebase – otherwise someone needs to fix the conflicts.)
In my personal experience, we are indeed sometimes limited by the a limited bandwidth of people doing reviews and taking actions on PRs (reviewing a proposed change with high quality standards can be a lot of work), and more contributions could of course help – note that most people doing reviews today do so on their free time, or at least instead of work they would get more recognition for; in particular it is very rare to have “please review PRs” on your job description.
There are a few cases of discussions ending up with no consensus, because we don’t know of a solution that has no downsides giving us pause. These issues can be blocked for years, and then revisited when someone comes with an idea that is clearly a big advance over the existing proposals, and then the situation can move fast. One example would be the let ... in .. with exn -> ... syntax that people have tried to propose in various forms over the years, have stalled, and were swiftly replaced by the match .. with exception ... construct which is better on all counts. But there are not “many” issues blocked in this way – fortunately it’s an uncommon situation.