Because they’re a specialty product sold to businesses not mass produced products sold to budget-minded consumers.

I also doubt they’re technologically superior as they’re just designed to display a static McDonalds menu for 18 hours a day, not play Dune in HDR at a massive bitrate. I’m no fan of tracking or similar corporate bullshit surrounding advertising but you’re making a lot of (almost entirely) assumptions here about these signage displays. You’ll likely be paying more than 2x the price of a comparable model considering these are likely equivalent to Black Friday TVs.