I've been thinking about this question for many years, and today I came upon this amazing question, Why didn't fluidic space crush Voyager?.
Part of the accepted answer is:
It is safe to assume there are similar physical forces such as gravitybold added, since their technology, while alien, seemed quite functional and effective in our Universe. This implies Species 8472 must be familiar with the properties and cosmological constants of our Universe if they are different than their own.
Sep 10 '12 at 8:54 Thaddeus
One astounding possibility is found in the comment
If the fluid fills the entire universe, then there is no region of significantly greater density for it to collapse upon. There is a uniform gravitational force pulling toward any and every part of the universe, but these all cancel one another, so in the end there is no net force.Jason Patterson
Can we say why didn't fluidic space collapse into itself eons ago?
The (as yet unclear real world) repulsive effects of Dark Energy may be another perfectly acceptable solution.
If this problem is deemed a duplicate/speculation I'll remove it.