Probably realized the USAF's Manned Orbiting Laboratory as a surveillance station wasn't going to work very well. Taking film pictures in orbit, having astronauts look them over and picking the good parts, then scanning the good parts with a slow scanner was a marginal idea. Transmitting all the data to the ground was much more useful.

There was a USAF thing for "we must control the high ground" in the 1960s and 1970s. The USAF had a space school during the Mercury-Gemini-Apollo years. The USAF wanted manned fighter aircraft that could reach low orbit, and proposed programs for decade after decade. It's a USAF thing. If you've had any involvement with the USAF, you know that there are pilots, and there's everybody else. The pilots are in charge. (Among the pilots, there are fighter pilots, and there's everybody else.)