High turnover in any sector is terrible for business. This is true even for relatively "unskilled" labor: informal, often unwritten practices between workers are essential to any kind of collaborative work. See the "slightly different sense" here: https://en.wikipedia.org/wiki/Work-to-rule
From what I can tell, I-bankers put in their time and either rise to a cushier role within the bank or they get into something else.
Juniors are judged by long hours and making sure their commas are perfect (in documents rarely read by clients) because there is nothing else to judge them on.
Like, Musk abuses his engineers who meekly accept that sort of thing. The theory that finance people standind up to it is something bad is absurd.