There's a difference between "can't figure out" and "can't be bothered to". Tier 1 teams have the analysts to figure him out; that's not a question. Top tier analysts are how the pros learn optimal ways to play their agents. There's just no reason for pro teams to look into Harbor yet. If there's a meta idea that works better than anything else out there, what's the point in trying to switch things up? This has long been the mentality of top teams in VALORANT—stick to what's safe, stick to what works. The few teams that played Harbor last year are teams like Karmine Corp, FunPlus Phoenix, and Nova Esports... teams that generally care less about what's meta and try to go for something unique. Teams would never borrow comp ideas from teams like that unless they just happen to align with future meta ideas (such as KC's Split comp last year).
In any case, Harbor wouldn't in this current meta anyway. Not because he's a good or bad agent, but because the meta relies so heavily on certain agents meshing together. Harbor works well with Yoru, but there's practically no synergy with Breach or Tejo—hence why you would practically never see them in the same comp.