Clearly shows that either no one understands the whole picture anymore or that it became so diverse custom, that this is the only way of handling this now.
I think though that these companies are more business companies than tech companies and move themselves into this nightmare.
It's even more wild when you realize that other similar-sized enterprise companies don't have all that and either leave bugs to sit around for decades, or randomly break shit trying to fix them.
So I suspect the answer is: they need _at least_ 10x as many engineers to get things done as you would expect. Maybe more like 50x