The issue is the relative degree to which the worker and investor get paid, as well as the risk they take. It's not a law of nature, societies can decide this democratically.

Did they get paid for their work? Or did their employer keep part of their pay while engaging in wage suppression?

"But that's illegal!" Yes. It doesn't matter because wage theft is the largest class of theft in the US. If nobody stops you, is it actually illegal?

And why should investors get a perpetual part of the profit after buying in once and labour has to keep providing labour every single day to get paid?

Because labor takes no risks. You work an hour, you get paid a wage. Investor might lose everything they put in. See the dot-com crash or any startup that goes bankrupt.

If investors could not profit they'd just put their money in a vault.

Labor takes no risks? Hahahhahaha! Career risk looks exactly like capital risk, with the big difference being that it is uncompensated.