Upto this point (in time), plasma drive is the most efficient (direct) converter of fuel into thrust, by electrifying it, in Traveller.
But even two and a half times efficiency still ensures it's a gas guzzler, which the stereotype of ye turboprop somewhat contradicts, for a regional airliner, or military transporter.
Also, it takes up a larger percentage of the spacecraft.
Now, reactionary rocket powered spacecraft tend to work out for intraplanetary, orbital, and lunar, transportation, since there is sufficient gas in the tank, and the cost of that is balanced by lower maintenance ones, and capital outlay.
Being within or near orbit, doesn't really make chucking out atomic warheads out the rear cargo hatch, to act as propulsion, appealing to the local electorate.
And, I suspect, atomic warheads aren't cheap.
Lightships might qualify, on the basis that if powered by an active fusion reactor, it's use it or lose it; but, I don't think it's been given the Mongoose treatment.