Why are movable rocket thrusters not used in airplanes?
Any time the question is "why don't we have...", the answer is almost certainly in the trade-off between weight, maintenance cost, fuel cost, &amp; utility. If it weighs a lot, needs maintenance, burns fuel, and will only be useful once a decade, then it just is not productive.

Putting rocket thrusters on a plane will be heavy, meaning fewer passengers, or less fuel or cargo on board.   All that extra weight has to be flown around, requiring fuel.  They would need regular maintenance checks, which is another cost.   And they would only be useful very, very infrequently (on most planes... never).

So, safety issues completely aside*, it is just impossible to justify adding new equipment for a once-in-a-lifetime scenario, which can be better managed with good maintenance, good training, and good planning.

This same line of reasoning goes for "why don't more airplanes have parachutes", "why don't planes have anti-missile systems", "why don't planes have airbags", and many other random items.


*Safety issues are a big deal with rockets.  Rockets are a controlled explosion.  What happens if that explosion is not controlled?  What happens if the rockets are triggered by accident, or blow up all at once?  Even if rockets passed all the tests of utility vs. costs, they would still increase risks to the plane, rather than decreasing it.