If those games are against other managers, I think it's just a matter of tougher competition. 80% teams usually put forth very little effort. So while your condition and morale are average, you're far more likely to play someone that also doesn't address that stuff.
A 120% requires some dedication (unless tanking) so these managers are likely to account for those things, plus know better tactics, develop well-trained (or mutant) players.
If the games are against bots, then idk. Perhaps, Nordeus might be doing something to the engine.