For starters, the 757 seats are typically only installed in a "pair" configuration hence the 2-2 layout on the 757. In order to transplant those seats onto the 767 you'd be looking at either a 2-2 configuration (with an unreasonably wide aisle on-top of being uneconomical), a 2-2-2 configuration (like on AM's 787s which wouldn't fit on the 767) or, like you mentioned, a 1-2-1 configuration which would still result in a wide aisle and awkward configuration.

On top of that the 757 seats are certainly inferior to the Thomson Vantage seats on the 767; physically shorter seats, significantly more restricted footwell space and oh, did I mention the lack of direct aisle access? It seems a plethora of people on here have simply come to the expectation that a reverse herringbone seat should be present on each and every plane... simply not going to happen. The 767 seats may not be the "best in class" but they're a perfectly fine product for that aircraft.

And for the one (or few?) I saw referencing the AA 767 seats... They're identical. Same manufacturer. Same layout. But no TVs.

The final portion of your comment is asinine and nearly not worthy of a response. Does anyone think DL (or any sensible organization at that) is going to choose a product based on how many nonrevs they can fit?