There are so many factors in this area I definitely don’t have it down.
The ATSC has 18 standards, 12 in SDTV and 6 in HDTV. I believe 1080I is their top HD standard. This does not mean 1080p is not out there or available, they just don’t list it under the 18 standards
Broadcasters have nothing in 1080p but I believe film does.
True HD is only supported in 16.9 AR while SDTV supports 4:3 and 16.9.

Broadcasters DO NOT want 1080p because it requires full bandwidth of 24Mbps. They would be perfectly content leaving 1080I as the top supported standard boxtop or integrated on any display.
The Grand Alliance supports all Digital Standards including 1080p, although I believe it is designed to be primarily compatible and geared towards computers rather than NTSC displays.

Broadcasters lose advertising revenue if they carry 1080p so stations don’t want it. By using 720p they can carry 3 or 4 stations per 40MHz frequency instead of one as 1080p requires.

The Academy of Motion pictures supports higher resolutions. Once consumers see 1080p on displays with excellent de-interlacers and scalers , - however the source is force fed and then eventually natively. What do you think they will desire?

As I see it everyone went nuts over the 18 formats designated as too many flavors for display manufacturers to sort through in choosing the capabilities of their current models.. But what I perceive to be coming is a shakeout effect of what consumer’s demand… As they see more and more of the higher resolution feeds they will want it, and the trickle down will cause 720p and 1080I to be supported on all displays at a fraction of today’s cost. But will that satisfy videophilles. Never… and 1080p has the potential for more lines of resolution. And will there be something ‘better’ after that. Eventually yes. And on and on through the next ‘super’ DVD (or like medium) etc which can make use of increased LOR.

Just my current take on the situation but its muddled and convoluted. Someday the pricing on 1920H will be south of a car.
Looking forward to it.