Who said they were phased out by TIE interceptors?
ROTJ and common sense say so.
Why does the B-52H, last built in the 1960s, still make up nearly half of the US heavy bomber force? Why does USAF still fly versions of the F-16, initially developed in the 1970s, despite the development of more advanced airframes such as the F-15, F/A-18, and F-22? Can’t seem to figure out what common sense you speak of.
Don’t forget that the F-15 (and A-10, which is still a workhorse) is older than Star Wars, the F/A-18 is older than Empire, and the F-22 is as old as the Special Editions. Plus, all of these planes serve different purposes for different branches of the military. The same is true for Star Wars:
The TIE Interceptor serves as a specialized air-to-air fighter while the the normal TIE Tighter is more of a multi-role craft from all the canon I’ve ever known. Same as the TIE Bomber is a specialized bomber, or the TIE Striker is a specialized atmospheric fighter/transport.
No major military just has “one” model of fighter that they replace continually. In World War II there was the P-51, the P-40, the F4, F6, and F8, P-47, the F4U… and that’s just some of the American planes I can think of off the top of my head, several of these went on to fight in Korea as well and some saw active service until the late 60s and early 70s.