It may not look like it now, but steam is struggling to maintain relevance, if they were to only host professional made games at this point then any platform that built itself to cater to the indies would end up crushing steam. Don’t think about this in terms of hours played and dollars spent, think of this in terms of hours spent shopping. People love the hunt for a new game and say what you will, I know I can download anything by EA and have the same repackaged feeling I get when I watch anything out of the MCU now.
And while I think some level of QC may be a good thing…a move by steam to only cater to those who could pay such a fee would be the death of steam.