No he eventually became a full professor too.

"He began work in 1949 with a $5,000 salary(equivalent to $68,000 in 2025), maintaining this position for several years. By 1952, however, he was making more money as a writer than from the university, and he eventually stopped doing research, confining his university role to lecturing students.[g] In 1955, he was promoted to tenured associate professor. In December 1957, Asimov was dismissed from his teaching post, with effect from June 30, 1958, due to his lack of research. After a struggle over two years, he reached an agreement with the university that he would keep his title and give the opening lecture each year for a biochemistry class. On October 18, 1979, the university honored his writing by promoting him to full professor of biochemistry."

Indeed after becoming a giant of the field in the 1940s and 1950s, when he wrote most of the novels and short stories we know him for (Robots, Foundation and Empire) he took a long hiatus. In the 1960s and 70s, as far as I can tell, his meager sci-fi output consisted of some short stories, a couple of novelizations of sci-fi movies, and a standalone novel (The Gods Themselves).

After Sputnik he focused on science writing, believing that to be more widely useful.

He only returned to writing more Foundation, Robots, and Empire novels in the 1980s.