That is due to wage stagnation, not prop 13.
> Median household income (in 2019 dollars), 2015-2019
> Cupertino: $171,917 [1]
> USA: $62,843 [2]
[1] https://www.census.gov/quickfacts/fact/table/cupertinocityca...
[2] https://www.census.gov/quickfacts/fact/table/US/INC110219#IN...
It’s because wages haven’t grown in line with investment returns over time.
This is not controversial, and is nothing to do with Prop 13 or whether Cupertino has a higher average income than other US cities.
That is due to wage stagnation, not prop 13.