If you have one developer, he or she will be the expert of that project. If you want a team of multiple developers, and it's infeasible to have any one of them

If you have one developer, he or she will be the expert of that project. If you want a team of multiple developers, and it's infeasible to have any one of them be an expert of the entire system (let alone all of them), then the amount of planning and standardization needed increases quickly. The bigger the team is, the stricter the rules for style need to be, the better the documentation needs to be, etc. I would expect the cleanest projects to be ones written by single developers because A) these projects will typically be simpler than the ones that require teams, by nature, and B) they will be undistracted / avoid the flaws of design by committee. Think cinema auteur vs. a Marvel or Disney film with an army of writers. Go lang is a good example of identifying and addressing the problems that appear when your code is managed by a large team.