I would imagine there's sufficient scope for it - of course it would likely apply more to a series set in the earlier days in general.
I would find it hard to imagine that United Earth operated and went about things flawlessly from it's inception. A bureacracy THAT huge is not going to be able to please everyone all the time and even the term 'United' seems to have been only so after a fashion. If I recall, there's evidence that not all countries on Earth signed up to it immediately and that some took longer to join over a period of several years.
One might wonder why that was?
Perhaps some of the terms (which I would have to imagine there was, there's never NOT) attached to joining the United Earth Government were such that some countries didn't want to sign up so quickly?
Or that sort of potentially rather severe (not in harshness, but in scope since it does suggest BIG Government) globalisation and centralisation of power might not be to the liking of those who sought a slightly more individual and personally free approach to living. In the early days when it was all unknown and still to prove itself as a method of Governance that could work. They seem quite happy with it by the 24th Century and in the core worlds like Earth itself but by then it's had a couple of centuries and few generations living under it to get used to it's pro's and con's. Not that we know for 100% what they may be, but they likely would be present, though even the situation that developed with The Maquis seems to illustrate that individuals can easily rebel on their political leaders even in the 24th C. So it would surely be a factor in it's early days.
Maybe they preferred to leave so that they could fashion their own destiny and version of peace and prosperity on a new world, without having to live under a type of structural government they didn't want to.
There's a hundred and one possibilities.
Who knows for sure, it's all another very undefined period in the timeline.
'If the Apocalypse starts, beep me!' - Buffy Summers
'The sky's the limit.....' Jean-Luc Picard, 'All Good Things'
courtesy of Saquist