does anyone know why EVs dont use gears for more efficiency?
That said, there usually is some kind of gearing as I understand it, but a static reduction, not in the way a combustion engine car is.
So in those cases, people do sometimes fiddle with gears while driving, mainly for fun I guess; but most often they just leave it in 3rd and drive that way.
(A dual motor design could simulate the benefits of two gears by having different final drive ratios for each axle.)
Combustion engines have some limitations that require gearbox to mitigate them:
https://x-engineer.org/automotive-engineering/drivetrain/tra...
Electric engines have none of those limitations, so no need for gearbox.
Although the Porsche Taycan does have a two speed gear box which gives it more top end performance: https://www.youtube.com/watch?v=ItCGU7BTBv8
What most don't have is gearboxes to change the ratio. The exception is the Porsche Taycan with 2 gears in gearboxes, the second gear slightly improves the acceleration at high speeds and improves the efficiency at high speeds. Accelerating super fast when you are already above the speed limit is not very useful for most people so most electric cars have no gearboxes, despite the slightly better efficiency. It's too complex and expensive. An electric engine has a lot of torque, you need a really good and expensive gearbox to handle it. It makes sense on a Porsche, but not on a Zoé.
Tesla has another alternative on the cars with two motors. They don't have the same gear ratios. The rear motor is used more at low speeds and the front one is used more at high speeds. It's a bit less fast than the Porsche solution but much simpler and cheaper.
In both cases, having different gears indeed improve the efficiency. I think the Tesla solution is very clever but requires two motors, so it's not perfect either. Most eletric cars have a single motor.