I don't know if that's generally true though. I understand that in a game like Battletech the weapons have ridiculously short ranges.
Ooh, ooh! I actually have an explanation for this if I ever try to do my own mecha setting!
The short version: forcefields which do not transfer momentum and which do create strong EM interference.
Like, the various reasons Battletech is silly are:
1. Why pilot mecha instead of drones?
2. Why bipeds instead of planes or tanks?
3. Why are ranges so short?
My solution is that basically that the same tech that lets you do FTL (by creating a bubble in space and shunting everything inside somewhere else) can be used on a smaller scale and with lower energy requirements to basically put forcefields around objects.
The thing is, the forcefield has to be a complete shell, and it's almost entirely non-permeable and just a field, not a physical thing that can rotate. It can
flex a little bit like if you're moving joints, but if you put a forcefield on a tank, it can't get traction to drive. If you put it on a plane, there's no way for wings to get lift because there's no airflow. But there's enough friction with objects that if you put it on, y'know, a mech, its feet can get purchase, and it swings its legs forward instead of needing to roll.
And the forcefield traps heat, which fits a big trope of Battletech of mechs shutting down and becoming vulnerable when they get too hot.
Also, forcefields mess up complex electronics. Within the field, you can't possibly build a self-operating AI to control the robot. You also can't get very precise signals to transmit much data - scratchy radio can get through, but not with enough fidelity to pilot a drone.
Likewise, battlefields would usually be filled with a lot of EM interference, so you can't use remote controlled missiles or even smart missiles. This pushes engagement ranges much closer.
There would be three main classes of weapons that have different perks.
Lasers go through forcefields, but produce a lot of heat when you fire them, and they don't do
much damage.
Missiles pepper the target in multiple locations, which forces the forcefield to have to modulate to resist impacts in numerous spots at once, which is more of a strain than single big hits. Enough simultaneous hits will overload the forcefield, causing it to be weak over a few spots.
Ballistics deal the biggest punch, but you want to conserve them until after the shield is down. So ballistics would have longer range, but you usually need to be within the (1 km) range of missiles to have a good shot of taking down the shield so your ballistics can do their job.