The reason I could see for reversible angle grinders is so you can control, kinda, where the sparks fly, and also you can use the rotation of the wheel to force the workpiece against the shoe. Maybe regular users of angle grinders don’t care about that, but when I use the M12 cutoff tool, it’s pretty handy.
A brushless motor running in reverse can be just as efficient as running forward. It’s all about when the electronic brain chooses to flip the electromagnets, right?
A reversible jigsaw, recip, or sander doesn’t sound useful, and in a circ, it might be dangerous. But a reversible router could be useful, because the rotation direction determines how you feed the work to the tool (or the tool to the work.) But you’d need left-handed router bits, which to my knowledge don’t exist, probably because reversible routers don’t exist (yet).
But grinder wheels don’t care about direction. It’s just the tool.