The Air Force was studying RTLS as part of the ARES (Affordable REsponsive Spacelift) program in 2005 (Which was the result of 1992/1994-era discussions on "spacecast 2020"):
And I don't see any rocket actually coming back with an orbital payload? Where's the demonstrator? Like that quiet supersonic thing Lockheed is demonstrating.
Even Lars didn't deliver at the first attempt. So it's not like it was something available off the shelf. Like some cryptography library you include in your code.
In fact it was one of the reasons red dragon was cancelled.
The group studying hypersonic retro propulsion of boosters at NASA was let go because that's what SpaceX did to land