You are playing against BBL.
You do not ban Ascent because you can counter it.
BBL instantly picks Ascent.
You lose against BBL.
You ban Ascent next time you play against BBL because you're not stupid.
it goes more like this:
You are playing against BBL.
You do not ban Ascent even though you will probably lose it.
BBL instantly picks Ascent.
You pick a strong map for yourself, and get two bans in that benefit you. You make sure the third map also favors you.
You win, because BBL can only play Ascent at the highest level, and they are nowhere near as prepped or proven on other maps as their Ascent, as it is their gimmick