Look at Newton's Second Law of Motion. F = m A
No, I mean REALLY LOOK AT IT.
F = m A
The FORCE you need to give something an acceleration of A is (MASS) x (A).
If your object is moving with a steady speed in a straight line, then it has no acceleration. A = Zero.
The force it takes to keep it moving that way is (mass) x (zero) = Zero .
An object that's moving in a straight line at a steady speed doesn't need ANY force to keep going.
Force does not CAUSE constant uniform motion. Force CHANGES motion.