Markets don't move by magic. They move by the aggregation of thousands and millions of transactions. And yeah, sellers and lenders absolutely incorporate their taxes into prices.

I see what you are trying to say about capital gains taxes not being in the "price" of securities. But they are in aggregate because taxes inevitably have to be paid. The whole market can't go up without transactions pushing it higher. And all transactions that make profit get a portion pulled out for taxes. They quite literally act as a damper on how fast a market can move.