I would have to assume that OP is lamenting the fact that the games themselves are not running natively on open source, and the existence of Proton detracts from game developers / publishers targeting Linux/OSS because now they don't really have a need to.

Or he could be lamenting that the games themselves are not open source, but I haven't heard many of even the most die hard OSS evangelists suggest that AAA gaming content should be open sourced.