I am thinking if you play 45s like this, you must maximize and somehow get a/i on river.

The only hands he bets on the river (that you beat) are sets, aces up, or nut straight.
He is probalby never raising w/out a (better) backdoor flush or KT - so shove.

I don't understand why the A is so much worse than say, T of spades. It makes (in his eyes) less likely we have a flush, and MORE likely that he makes 2 pair.

I guess if he never makes crying call with 2 pair, then just value bet. But you have < PSB behind, so isn't a push a value bet?

What subtle thing am I missing?