No one has mentioned this yet, but it's a bit of a contributing factor--lack of adapters for other fast charging.
Most of the country that is not California or a few other really large cities still don't have these crowding problems at the Superchargers. I still look at my local Supercharger when I drive by and am excited seeing a car there.
So it is mainly in the very large cites that have clogged Superchargers. Well, guess what really large cities have? Other charging stations. But up until right now, the Model 3 could not access CHAdeMO or CCS stations throughout these cities, so they were all getting funneled into the very limited number of Supercharger locations. If some other choices were available, this would be a supply and demand problem that would sort itself out, and people could go to less used stations.
Just in the past week, Tesla has created a new firmware version that will let the Model 3 use the CHAdeMO adapter, but it is just barely beginning to be deployed to the fleet, so it will take some time to get that choice capability out there and still won't enable CCS stations.
There is also another factor that
@Big Dog is alluding to--uneven distribution--but specifically because of price. In the smaller cites, incomes are a bit lower on average. For the first few years of having our Model S, most people I talked with thought it was cool, but couldn't conceive of buying a car that cost over $70,000. That's kind of outrageous for areas that aren't like L.A. or San Fran. A lot of flyover country is that way. But they will somewhat reasonably tolerate buying a car that is $30,000 to $40,000.
Sooo, California was getting kind of saturated with early S and X buying. Now, we are into the later phases where a lot the middle of the country who couldn't afford an S or X are buying Model 3s in areas that still have pretty good excess Supercharger capacity. So the generalized ratio number climbing shouldn't be quite such a nationwide issue.