So one can measure several different things without fiddling with leads and contact jacks.
Can you explain your use case more?
But in general, I guess you didn't look very hard, since most models from the major bench DMM makers (Keysight, Keithley, Tektronix/Fluke) have switchable front/back inputs.
Keithley still makes lots of meters that accept input switch ("scanner") cards or switchboxes to do (industrial/lab/factory) testing at high speed — these can scale up to dozens of inputs.