When I said that it "doesn't prevent anyone from participating", I was only considering the editors who are interested in writing about a wider variety of topics.
For better or worse, Wikipedia frowns on editors who are only interested in editing articles on one topic. There's a page for that:
https://en.wikipedia.org/wiki/Wikipedia:Single-purpose_accou...
This is because these editors usually have a conflict of interest, and must make an extra effort to keep their writing free of bias.
Policies aimed at improving the quality of articles also tend to reduce participation. It's a trade-off, and I don't know that the optimal balance would be.