KK - Would he shove with a worse hand?

I find this a very good question because I do not know.

Now here is why I don't know:

I think on the river the chances you are beat are 95% .. the pot is 114 and you have to pay 57 so pot committed I think?

Now the part I do not know and don't understand:
If you almost certainly know you are beat *why* do you have to put in another 57 BB? What is the theory/math about being pot committed in this situation?

For me the river decision seems quite easy.
You need 25% equity to call. Call Call Donk - line is very often very very strong. Flush just got there and any A and 6 makes a straight.

With what hands villain can call flop and turn? He probably calls our 3bet pre with some pocket pairs, AQ,AJ, maybe ATs, KQs and then some suited connectors?
When he calls the turn I would say he has very likely a flush draw, straight draw or a QX hand. If he had flush or straight draws those just got there OTR. If he has QX most of them are AQ and those just got a straight. If he has KQs, there is only one KQs combo that we beat.

Based on his stats and that he calls your bet on the flop and turn i put him most certainly on AQ. As said above, the line that he took, the weaker hand that he could be representing on the river is a set and we don't beat it.
Given that his range consists mostly of Ax combos and PP, i think we have to fold. Unfortunate to get this action with KK but is poker 😆
Keep up the work.