While you're not "limited", if the selector one is in such a state, the hot/cold are likely not much better and may fail quite soon. It's probably best to bite the bullet and replace the whole thing while you're at it instead of doing the same work 3 times in 3 consecutive years as one valve after another fails.

Largely, the matter of size, total volume of refrigerant.

Liquid is incompressible so you can't really run Carnot cycle on liquid alone. Gas alone, due to low density, has very lousy specific heat - can't transfer much heat per unit of volume. So, for refrigeration on gas alone you'd need lots and lots of gas volume to circulate quite fast, making your freezer unreasonably big.

By only keeping a relatively small part of the circuit filled with gas, you assure a decent amount of slowly moving, efficient heat-absorbing coolant (cold liquid evaporating in the evaporator) and heat-expelling coolant (gas compressed into liquid cooling down in the radiator), while only a small part of the circuit carries large amounts of gas, fast, between the evaporator, through compressor, into the radiator, providing the pressure transition required by the Carnot cycle.

If it was a moon, then yes. This cat is not losing weight anytime soon.

Waxing gibbous.