They are not irreplaceable but it would create the sort of inverse "moral hazard" that might stop these practices, which are apparently what's being protected.

Hard to imagine that the Chief Financial Spreadsheet Monkey is irreplaceable. If you want someone irreplaceable, I'd look at the COBOL programmers.

The revolving door between the financial sector and our government- if they jailed people now then when it's their turn to get rich off of their government connections they might risk jail.

they did charge them: https://www.cftc.gov/PressRoom/PressReleases/8013-19

It’s bad for campaign donations and bad for future highly paid job prospects in the financial industry. So politicians and agency workers have strong incentives to not be too tough on banks.