That's because most probably fate spammed with no concept of what most of the skills/combos do. I also had a few runs where the Drg didnt use HV and spammed ROT only, and only used FT combo on single targets. And one smn who only single target DOT and no shadow flare etc. Also a BRD who would use Battle voice without a song and said it increases all the parties stats (as a FC member told him).

So its quite common to see these in roulette. The only thing you can do is coach them but it seems 75% don't listen or tell you they know what they are doing.