It is because it is.
There’s no point in questioning it. If you don’t like it, open the source and change it.
But in the end it won’t really change anything.
Units of measures are fluid.
They can always be scaled and transformed from A to B so it really doesn’t matter what the base unit is considered to be.
Except that if you go imperial then you can’t *100 to get to a meter, which potentially makes things harder.
However it really doesn’t matter.
Speed velocities are represented in m/s for convenience.
Scientifically when looking at bullet trajectories and the like scientists user meter per second.
Americans use feet per second.
Usually if you look up the data on an ammo box (the few that have data tables that is) muzzle velocity is reported as both m/s and f/s
Since the times we enter in velocity is mostly related to projectiles, the fact it’s in m/s is a convenience factor of not having to convert it.