Imagine that in some years only ~50 bitcoins will be bornt every day.
Tx fees over the last 10 blocks:
630810 1.20075488
630809 0.97858807
630808 1.54706548
630807 1.65427222
630806 1.74193119
630805 0.06098868
630804 0.55885389
630803 1.23086252
630802 1.46149062
630801 1.79528729
Does this answer your troubles?
Will miners that will mine blocks in the year 2136, be happy with their tiny reward + fees? If they can mine, it means that they will afford the electricity meaning: 1 satoshi will be much more expensive than now.
Mining is always a thing of costs.
If the reward is 1 mil$ a day, miners will be able to spend half a million on electricity.
If the reward is 100k$ they won't be able so they will mine with less gear, spending only 50k$.
Miners don't decide the price, the price decides what miners do.
Think of the oil industry, it's the same, the price goes below 20$ wells are shut, the price goes above 100$ everyone is drililing.