Game versions with less than 7 reviews don't get a MetaScore. That hurts the Xbox numbers, since the more popular consoles (currently PS4 + Switch) get more reviews.
Some good rated PS4 and Switch games (with more than 6 reviews each) also are available for Xbox (with 6 or less reviews).
Therefore the situation for Xbox gamers is a bit better than shown by the numbers.
And with tie ratios of less than 20 games per console, "only" 300 XBO games with 80+ ratings shouldn't be a big problem. There are more than enough good games on all platforms for most system owners.
Ah I see. I assumed you had the common sense to add to Xbox any game that got good reviews on the PC, PS4, or Switch side. In that case Xbox isn't as bad off as this graph shows. What do you mean by tie ratio?
Also a few questions about your graph...
1. Do game expansions count as an individual game? For example if WoW gets a new expansion does that count as +1 game for PC? Or if Sword/Shield gets new DLC does that count as +1 game for Switch?
2. What's the ratio of 2D Indie games to fully fledged 3D games?
3. Do game compilations count as their own games? For example: Do all the games in Super Mario 3D All Stars count as one game for Switch or as three games? If a game gets released in both a compilation, and in a standalone release, do both the compilation and standalone release count as a game? Would Control and Control Ultimate Edition each count as +1 release for their respective platforms?