There’s a trade-off between having a manual vs. automated process in the best of circumstances. You might think intuitively that an automated process would be easier and more reliable, but depending on local factors for each of the databases, there might be issues like availability or locking that could make an automated solution more “fragile” than simply having an employee with domain expertise doing an update on a schedule. Reliably automating a process like this would require a lot of careful QA.
So throwing legacy systems into the mix would just aggravate this further. It may be that the cost/benefit of automating this just isn’t there. If it’s cheaper in terms of salary cost to do it by hand for N years than the one-time expense to automate, it may just not make sense to automate. (Obviously over an indefinite time scale it would almost always make sense to automate)