I can only speculate Valve's reasoning, but there are a very select few games that require actual case folding and not the simulated case folding that wine offers. I know of literally only one.
I have a Legion Go. I don't have the specs handy now, but the SSD was rated fast enough that I suspected compression would harm my overall performance.
All Linux filesystems will by default allow "TEST" and "test" and "Test" to exist in the same folder, which no Windows application is ever intended to handle. Wine works around this by default.
Windows apps are expected to handle case sensitivity gracefully in non-FAT filesystems.