This is a double-edged sword. I can admit up front that don't have a very flattering view of the most popular British commercial news outlets. But they're popular.
So, in a way, if BBC wishes to remain accessible among people who are used to... certain popular British news outlets, it shouldn't isolate itself in an ivory tower. If BBC's domestic target demographics have a poor reading level, that's likely more of a Britain problem than a BBC problem.
There's probably also an aspect of serving populations inside Britain who don't speak English as their first language. The BBC's mission statement[1] also mentions mirroring Britain to the world, which likely increases the need for accessible language.
This is a basic soft power strategy anyone seeking global relevance should pay attention to.