Open source OS's also don't do anything for the typical person in a feature sense so there's way less to go wrong and way fewer users to ever discover/report is

Open source OS's also don't do anything for the typical person in a feature sense so there's way less to go wrong and way fewer users to ever discover/report issues. Non-technical users want to run specific hardware like new displays or accessories or use apps like a game or a specific commercial program, not run an OS. Without those users, there's no need to grow the feature set as aggressively.