I worked for an organisation that had been involved in the internet from the very beginning. I really only used the the email system ( I probably used others without knowing it) and it was awful. For example, if you accessed it from outside the organisation’s own computers you could never access it again from inside. It was an utter mess!

I was told the reason was that it had been put together over decades with individual bits which did not quite work together. Although one new bit would work well with the existing one, it never quite engaged with another new one tacked on a year later.

Whilst I know nothing of computers if I had to guess: BA has the same sort of problem.