The SA80 has had a storied history. Until the A2 iteration, with the help of H&K, the rifle had very serious reliability issues. But early in its development that actually wasn’t the case.
Before the U.S. swung NATO the way they did in small arms development the Brits were working on a bullpup that would eventually be broken enough to become the SA80/L85 first iteration. But prior to that the prototype rifles they were developing actually worked alright.
The problem with giving a bunch of good engineers an engineering problem that they have no practical experience with (IE: small arms development) is that they just do not possess the familiarity to think of the small items like ergonomics against web gear or how it will run when snow gets packed into the space behind the trigger guard.