Just as when DAK was built, Universal is worried about cannibalization with the 3rd park. If they had the space, they would much, much rather expand the existing parks. Unfortunately (at least they consider it unfortunate), they have to expand further in order to maintain healthy growth.
D23 2017 caused some alarm bells to go off inside Universal. They're taking a wait and see approach to Disney's pipeline. The thinking is that UOR may lose substantial market share as they are not the market leader. If Disney's projects have an adverse effect on UOR, and the Orlando market shifts heavily in Disney's favor, it will have an impact on future Orlando investment from Universal. I dare say, contrary to what many have said, the third gate budget is not locked down.
Whether it is a positive impact or a negative impact is up to the statisticians and what level of investment they feel will generate the best return on investment.
Other than the D23 bit, most of this does not line-up in any way with what I've heard and/or know.