It comes down to...
in BP canon After use a subspace drive needs chance to charge/cool down/reset (I believe derived from Kings Gambit in the FS2 campaign when it is mentioned in the (command)briefing stage).
This limitation can be circumvented by having a backup drive (called a sprint drive in BP) but only GTVA ships have these sprint drives and then only on select ships due to space and cost limitations.
So if a ship jumps in and is quickly jumped by a superior force (easy to plan with subspace tracking) the ship can't jump out for a set time because the jump drive is inoperable
If I recall, there were in fact cases where UEF vessels could have departed.
The first mission being a prime example, the Ironhide, I believe. The ship captain refuses to jump, even when critically damaged. I usually manage to save the ship, but if the bomber strike manages to hit, the ship just sits there and takes it. While I understand the reasoning behind the decision (Drama, consequences for failing, psychology of UEF captains, ect), it would be nice to see at least 1 UEF ship manage a tactical retreat under fire.
Granted, there is the last mission, but that isn't really under fire, but the looming threat of fire, and tactical overmatch.
