Sure, I'm with you there.
On the other hand, I've thought about this and there a couple of reasons to have everyone play 2-minute turns.
1) Player base fragmentation. This is not yet a hugely popular game. It makes it harder to get a match if the players looking for a game use different time limit settings. When there is only one option, everyone gets a game faster. Sure, you could agree in chat what limit to use, but this is extra hassle and not everyone likes doing it. Having a single limit just makes it a smoother experience out of the box.
2) The matches become a lot longer wth e.g. a 4-minute turn. In Blood Bowl a match (16 turns) usually takes around 1 h 45 min using 4-minute turns. I just had a match go for almost 30 turns. Imagine that with 4-minute turns.
I think Dungeonbowl is meant to be a more relaxed, fun and fast version of Blood Bowl. Having the games drag on longer would detract from this quite a lot.
Having said that ,I run out of time all the time. 2 min 30 seconds would be great for me

Your mileage may vary.