You can't fight physics. A gas-powered sedan weighed down by all the modern safety requirements can only get ~43mpg on the highway.
A hybrid boosts this to ~55mpg and also greatly improves city efficiency.
Above those numbers, you're looking at engines that are severely underpowered (1.0 liters) or is more EV than gas car.
> I personally think it's because vehicle manufacturers have spent the last ~20 years not really improving the core vehicle at all, and instead convincing people that massage seats and car play are actually important.
Well, yes. To please the American consumerist mindset, you have to keep inventing new features even if the new feature is a complete gimmick or just a subscription, or taking out physical buttons (e.g. all strictly negatives).
> If someone made a car that was comfortable, easy to drive, had plenty of storage and was super cheap to drive (like 3l/100km / ~70 US MPG) I'd be all over it.
At that point why not just wish for a magic horse that flies or something. 70 MPG is an EV number. You'll never get a gas car that gets that mileage.