As someone who just works in the development industry overall, and as someone who recently had a brief insight on how Fortnite developers build their code (bug symptoms, and one or another comment the devs do on reddit times to times), what I can say is that there's no such thing as "infinite resources".
There's a saying: "what 1 developer can do in 1 month, 2 developers can do in 2".
Meaning you cannot really just add more developers to a task, and expect it to finish faster, it may actually finish slower.
Also, you could have all the money in the world, but the gold supply is still more valuable and rarer than copper, and no matter how much copper you have, gold is still much better.
What I mean is that great developers are hard to come by these days, and the market is flooded with mediocre to "just competent enough" developers, not necessarily good developers (even if you limit to seniors), not even necessarily passionate developers, and good and great developers are scarce and highly valuable.
I have interviewed probably over 100 candidates myself in my lifetime, to either join my team or some other similar team, and have looked at the test results of probably 3x that (from a test I created, with one or another trick or difficult question, but mostly very simple stuff), and even when I lower the standards of entry, many still manage to surprise me negatively, and it doesn't matter if they have 2 years of experience or 10, or if they graduated from college or not, either developer has "it" or not, very simple.
In the case of Fortnite, it's clear that they may have maybe a few great developers there, but the rest is just competent enough to secure the job, and not any better.
I am sure they have passion, the game itself is very cool and really popular, but you can tell simply by how they build their things and the bugs which arise from such practices, that it's not exactly a place oozing with talent, in respect of programming at least. But generally speaking, no place is either way.
Having that said, UT99 is and will always be what boomed UE1 forward, and as far as projects of this kind, they don't want to promote what essentially is an extremely old game, and if someone had to monitor a community project to fix it and improve it, they would need someone very very trustworthy from the community AND someone who actually originally worked on the game or knows all its ins and outs, and those folks are either gone from the company or working as seniors on Fortnite, thus they indeed have no resources for this.
They cannot hire just anyone to keep a look on these things on part of their time, and anyone whom would actually be good enough to do this, would probably be good enough and important enough to be added to the Fortnite team as a full time job instead, because again, good developers are hard to come by nowadays.
Also, anyone good enough for such a job, probably wouldn't be interested in checking an almost 2-decade old engine, it would always to be to work on UE4 or newer.