Because it's a cantrip. The whole point of cantrips is that they can be used at will because they're not strong in the first place.
Sure, cantrips can generally be used at will and without using a spell slot, and this change means that for Mage Hand only the latter is now true and therefore it can't be used as frequently. But it still can be used three times per adventuring day, and personally I don't tend to find myself using it more frequently than that anyway so I was wondering what other people are doing with the spell that they need to use it more often for it to be useful.
There are exceptions where I'd occasionally like to have more use of Mage Hand, and I can envisage that in some circumstances I'll need to ration my use of the cantrip more carefully so I'd agree that it's not as useful as it was. And if the change is intentional, that's presumably because Larian thought it was
too useful in some situations for a free use.
I don't know whether I agree with that and will reserve judgement until I've played more of the game, but so far am still finding Mage Hand situationally useful and haven't found the once per short rest restriction nearly enough to make it useless.