One problem that I've seen in one such large company, and heard of from some people in others (FAANGs), is that there's no incentive to maintain these internal

One problem that I've seen in one such large company, and heard of from some people in others (FAANGs), is that there's no incentive to maintain these internal tools. Sure, they often start out as sort of amazing and there's a ship email and for 1-3 years a strong team, but you are unlikely to be promoted a lot polishing UI, fixing bugs and adding features or even support for new backend systems... so, eventually there's a skeleton crew maintaining an old tool, everybody complains how it's slow and sucks and behind the times, and then a brand new replacement is built that is going to fix everything. There's a ship email, people gradually switch to it, rinse, repeat.