My wife and I share a plugin hybrid and an EV. You'd think the EV is as loud, because you notice the air and tire noises in the absence of the engine noise.

But in the plugin hybrid, the change in noise is very noticeable when the car goes from pure EV into hybrid and the engine kicks in. It's specially loud when the engine revs up as you're accelerating, but even when the car is cruising, I can still hear the engine noise.

That is true above 50 km/h right? In many european cities you drive below that. In many French cities the max speed is even 30 km/h. Then EVs are much quietee.

I'd say the majority of the reason is no engine noise, but also keep in mind EVs are heavier than ICE cars. More weight means more road noise. Regenerative braking means they have significantly less brake wear than ICE cars despite the weight, but the tyres take more stress.