Because fuel is so cheap US cars are much less fuel efficient.
And European cars are more fuel efficient because of expensive fuel.
Arguing that Model 3 should only be compared against high performance sedans of equal size undermines the notion of very large demand in Europe. Here you are talking niche not mass market.
So when comparing fuel cost of typical European ICE hatchback to Model 3 the savings approach US levels.
I feel you're missing the context. In USA no one
really, really thinks about price of the gas. Yeah, it's a something one notices at the pump, occasionally is subject of conversation, but it's not real consideration. Not like in Europe.
In Europe, it's a real consideration in a way that it drives decision (of everyone) which engine to get (small and/or diesel), and that people will consider driving/no driving as a genuine choice for many a trip (even when they have a car).
Gold standard in operating car inexpensively was diesel, to the point that German sport sedans were being sold (and bought) with asthmatic 1.6l diesel engines. Many of my friends (until couple of years back) would have never considered anything but diesel.
And electric is still more economical than diesel. That's all that buyer will care about. Is there a cheaper way to drive? Nope. They'll calculate that it costs them equivalent of 3-3.8l per 100km on electric, even less with M3, with diesel 5-7l, small gas car 7-10l, and Tesla MS sized car 10-15l, and they'll be happy. Funny thing is, I feel(I'm not sure, but anecdotally) European buyers will
overpay for future savings. Diesel engined cars always (used to?) sell at the premium to slightly more powerful gas engine.
Again, this mindset does not present itself in the same way in NA*. I've lived it, and my brother still does, so I get it.
*Decades of cheap gas have conditioned us one way, and decades of even more expensive gas have conditioned Europeans another way. Gas price gap used to be even wider in the past.