It just needs crowdsourcing
The advantage of crowdsourcing is that everyone can participate. The disadvantage of crowdsourcing is that anyone can participate.
I can well imagine that Valve wants to do it themselves from a quality point of view, which in my opinion is not unimportant for the success of such a new device. To enforce quality in (for example) a compatibility list, you need very strict labeling guidelines. Guidelines to be followed properly. This doesn’t always go well with crowdsourcing.
ProtonDB has grown, in part because of its accessible character, and is now a useful and successful project in my opinion, but there are relatively many reviews from people who (I suppose) mean well, but whose reports do not always (fully) comply with the established guidelines, for a variety of the reasons. I absolutely do not mind messing around, but for a technical player, not a small part of the target group of this device, a potential source of annoyance and disappointment. Some notable examples: Platinum Rating with Comment “This game works great, just like I did on Windows after I made mod X!” The hacks work as if they were an original game. The unsuspecting couch potato expects an action game, but it won’t start. What a bullshit system! Or: “This game does not work” while the reviewer broke the distro himself. Or: “This game works fine”, but at level 12 there is a graphical effect (problematic for a proton) that causes the game to crash and you can never get past that point in this game, which of course you don’t see (immediately) if you play for an hour. Or: Gold rating with “This game just needs a no CD patch”, which you can search for yourself on questionable websites, which would be inconvenient on such a mobile device and might not be the best idea for someone who doesn’t know how the system works files. Taking averages from (recent) reviews is usually not a really good solution either. Standards vary (in my opinion: too much) between different user groups.
Additionally, the Steam Deck has a number of fairly specific requirements (is the text readable on such a small device, all input prompts for buttons that are also on the Steam Deck instead of a keyboard/mouse, etc.) important to everyone. Clear guidelines/protocols are needed for this, but it is impossible to consistently enforce good compliance with all this through crowdsourcing. Some people do not read (well), do not understand (well), or over time forget the intent. Not everyone is willing (or able) to strive for such a high level of quality, not forgetting that they are unpaid volunteers who do not receive periodic performance appraisal. After a day working with all kinds of rules and efforts, I can imagine that in the evening when the ProtonDB evaluation is finished, people adopt a more relaxed attitude and things that are (or may be) important to Valve come to the fore.