[OED:] A. 1. a. The action of turning over, in various senses: see quots.;
(Polit. slang) a transference of votes from one party to another.
I understand the morphemes 'turn' and over' and the literal meaning of 'turnover', per above. Instead, how does turnover figuratively mean the following? A business doesn't turn over the money received. 'Turning over people' sounds barbarous, but this noun is frequently used with neutral connotation.
[ODO:] 1. The amount of money taken by a business in a particular period:
2. The rate at which employees leave a workforce and are replaced
[I ask NOT about definition 3 for 'A small pie ...', which is literal enough for me to understand.]
Footnote: I don't think that this question concerns etymology, but if I've erred, please advise.