you shouldn't worry too much about what may or may not happen a 140 years from now since that is one and a half generation away from today! not to mention that with the way bitcoin is going, so far despite the huge decrease in the amount of block reward (from 50 down to 6.25) both hashrate and difficulty have grown to ridiculously higher values while miners are making millions of percentages more money compared to when the reward was 50!
This is solely happening because of the increase of bitcoin price right?
And what you stated is the increase from the past to the present but it still won't change the profitability of mining bitcoin and the fact that some miners have stopped mining because they can't get decent profit anymore.
Anyway, it's just a curiosity, and getting a satisfying answer will definitely stop me from asking the same question again. I won't make it until 140 years later for sure.
well based on what i have seen so far mining and how profitability and hashrate change over time is way more complicated than that. we can't really say this reason and that reason caused a rise or fall. there are many reasons involved.
of course price is the easiest to see and measure. but other reasons include the advancement of the mining equipment. for example during the 50
BTC reward time people were mostly mining with their CPUs and with the mining algorithms (SHA256) that might have not been that optimized. then it was GPUs then ... and finally we are at ASICs which improve every now and then. and "improvement" means miner spends less while producing more computing power and earns more money.
another influencing factor could be fees. although most of the times it is a small factor. for instance during 2017 miners were earning up to 5
BTC on top of 12.5 block reward in fees per block. that was around $30k to $40k additional income.