That is not really a good graph to make your point. 22% of the games would have to be made up at the end of the season or crunched in to other non travel days off. Double headers maybe? Even if your assumption that it is drier here and it goes down to say 18%? It's way too much. Portland would be absolutely stupid to build a stadium without a roof system.
No, it says that only 22% of games even reached a point where they decided that maybe the roof should be shut. Even in the middle of a game. It didn't say that it closed for rain that never materialized, or that there were high winds, or low temps or high temps (which wouldn't stop a game anyway, but if you have a roof, great!).
Phrased differently, only once in every 5 games was there even a remote chance that there would be rain, low temperatures, high temperatures, high wind, or lightning. That means, over the course of a season, 16 games where there's even a remote chance of having a delay or postponement. And if you don't have a roof, no one cares about playing in light rain, high wind, cold, heat, etc. The game goes on. Even in heavy rain, delays are preferred to the postponement. The most postponed-team in the majors this year was WAS, with 5. CLE, BOS, CHI/CHW, NYY, etc just play through stuff.
to me, in POR's fiscal and political environment, spending an extra $250M or so on a stadium to get
maybe 5 games' worth of non-postponement seems like a non-starter. I love the concept of a roof, and would want one if I was a billionaire building a stadium, but this is a nice-to-have, not a gotta-have, for MLB in PDX