The reason is simple but bit insidious - when there is enough "known reserves" of something, it is not economical to look for more. Once the amount of known reserves shrinks, it beings to be worth it and people start looking again. So it might always look like we have between two to five decades of oil or uranium or lithium or whatever.

Realistically, we will end humanity by burning oil a lot sooner than we will run out of oil.

Earth population will double by 30 years, so oil consumption will more than double to accommodate with the need of even more energy than before

Your perception of oil reserve is based on your needs today, rather than by projection

Oil is not an infinite resource, you need to think tomorrow

And that's without taking into account pollution, it'll more than double, earth size won't double, so what's gonna happen you think?

We can do like germany with this example, or we focus on something future proof