Could be misuse by passengers too. You won't have to look too long on here to find other displays of gaffer tape use on BA planes. "make do and mend" like this is quite a British thing, and if anything it's possibly also a case of the expectations of how long things ought to last not meeting the reality when unpredictable elements like humans start getting involved that even ridiculous amounts of over-engineering can't completely eliminate.
Where I do agree there is a problem is expecting 179 economy and WTP passengers to share 3 toilets. It only takes one of these to go out of action and once these start being overused they can go downhill quite rapidly. Even economy passengers deserve better.