The hashrate didn't grow from 1 petahash to 400 exahash becuase there was a $1000 pot to be earned a day.
Again, end scenario is that fees will be the only reward miners will get, you think you will have miners with the same hashing power on 600k a day tx playing each 20 cents?
Why must the number of miners constantly increase? Isn't it logical that at some point after reaching its highest level, it starts to decline?
It doesn't, the numbers are for keeping the hashrate stable.
There is a huge difference in efficiency between today's mining hardware and that of 10 years ago. Shouldn't we expect additional improvements in 5 or 10 years, for example?
Efficiency doesn't scale security proportionally.
The security of the chain does not only count hashes, it counts how much $ it costs to buy and run something to overcome the network and in this efficiency has little to say.
If the network is protected by 10000Th/s and
- it costs $2000 to buy a 100Th/s machine the attacker needs to cough up $200 000
- it costs $2000 to buy a 2000Th/s machine the attacker needs to $10 000

Well then you picked a very weird time to make this post. We're facing very high fees as bitcoin users in this moment, which as you're rightly pointing out is pricing out many bitcoin users and provides counter-incentive to use bitcoin for most types of normal transactions.
No, I picked the perfect time for it!
Because everyone was always saying when there are no more bitcoins to be mined miners will live on from fees!
When I told people what that meant during times when the fees were 1st/b they didn't show interest, when I told them the same thing now, look at the revelation, think of it as telling a kid about brushing his teeth, one time when he is just fine and does;t give a damn and the other time when he is on the dentist chair for an extraction.

If the capacity for transactions was simply increased, more people could be paying fees, albeit smaller, but this increased capacity would eventually balance out to higher fees in total.
Be my guest to open a topic about increasing the capacity, I'm grabbing my popcorn!
Common, do it, I can't wait for it!
As for me, I was just this week shown how it's physically impossible to have blocks larger than 4MB because only nodes that own a Titan computer and their own private global fiber optic cables would be able to cope with larger blocks!