Noone is complaining that they did not look through all their code for quadratic footguns. There probably are bunch of places like that, but they don't matter and doing that would probably be just a waste of time. Premature optimization is the root of all evil and it makes all sense to dedicate all your optimization on the 1% of code that actually matters the most - but this was the 1% that obviously should have been the target of optimization and was not.

The issue is that slow loading times was a contentious issue with many, many customer complaints (IMHO it was the #1 complaint) and during many years not once did they spend even trivial effort on trying to look into that complaint, and that's shameful. As the tostercx's article shows, if they had ever assigned any engineer a couple hours to look into why loading is slow with a profiler, that issue would have been easily found; the fix as described was a bit more tricky because the author did not have access to the source code, but within a company that would have literally be done within an afternoon by a single non-exceptional person. But they never cared enough to have someone look into it.