Well, mostly because sawk just doesn't have acces to u-turn. If it did, I'm sure it would be way higher in the viability list, but since it doesn't, it's just a worse scarfer than passimian, or even a bander, because never being able to get momentum on the obvious slowbro switch in for example (which usually easily tanks 2 hits from sawk or any other fighting type anyway), is extremely big. TLDR; It is very much outclassed by the other fighting types. That being said, it's speed tier being 5 points higher does give it a (small) niche.