In the U.S., it's much more likely that the custodians/janitors are getting underpaid.
If they were underpaid, they’d go work somewhere else they are not.
There is a near unlimited supply of mop-pushers in the world.
What if every place where they live is paying them around the same rate? Should every person be expected to move and uproot their life to find a job that pays them enough to live on?
Some ideologies construct an imaginary world with its own rules and and perfect ethical actors and then ignore that it does not map to reality.
I learned at a previous job that one of the biggest challenges in janitorial-services is the insane rate of turnover and difficulty in guaranteeing that a particular floor of a building has been serviced on a particular night...
US janitors can't go work in Sweden, where janitors are paid more fairly.
In what country in the UK id be doing very well to earn as much in London as the train driver - and they have a FS pension.