Most people are very helpful and quite understanding that as a sole indie developer, it would be hard to support all the configurations. But occasionally I get angry emails and negative reviews about game not running on Linux.
Given the sales (Linux is 1% of the total sales, Mac is 3%), I would say for an indie developer, it makes more sense to put Linux support on a low priority. It is unfortunate for Linux gaming community but it is what it is.
Also even though Proton has come a long way and has become relatively stable - occassionally there are some strange issues (like Steam Cloud sync fails, etc) here and there. But overall the effort is much lower compared to maintain a separate Linux build.