I agree the non-renewable resources run out much too quickly, but this doesn't mean they should last forever.
I don't know, it's down to how time is interpreted. Estimating a real world life expectancy of 84 means a game-year is 14 years.
An example lies in the Los Angeles City Oil Field, which unfortunately is quite old but the only oil field I know of in a city. It took 10 years to hit peak oil back in 1890, but we can be generous and assume technology hasn't improved that much (it has, but lets be generous!). It still produces oil, but almost none now. By 1961, it had less than 10% of the peak oil wells, so lets call that "depleted" even though we can argue back and fourth on when it should be considered "depleted" and what "depleted" should look like in Skylines.
So that gives us about 70 real years of production which is only 5 in-game years. That's crazy short but I think I was quite generous with the estimates.
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Edit: Now, a cool thing would be to allow Fracking as a district ordinance. Fracking factories should have a
huge radius of ground pollution, water pollution and it should spew polluted water into your pipe system, but it should produce oil anywhere.
I don't know of a good model for renewable ore. I don't think ore is depleted as fast as oil in reality, though. For something a bit fantastical, you could have Coal Mining as a district policy which has a huge fire risk and, if disasters ever work their way in, a coal fire (I wanna make Silent Hill!!!!).