Miners fees make up .3% of the money miners make, meaning that if the fees raised by 100x then miners would still only make a third of what they make now. Which in fantasy land means that miners just gracefully exit and cease to exist, but really means you now have a drop of hash rate and also a group of people with machines that make hashrate that got fucked over by bitcoin and have no wish for it to succeed.
You fail to understand the fact that the overall transaction volume is low now. When TX volume increases the overall amount of TX fees will also increase. Also when transaction volume increases the price of bitcoin is likely to increase as more commerce will generally mean higher demand for bitcoin.
There is a long time before the block subsidy will go away completely so bitcoin has a long time to see it's transaction volume increase enough to make TX fees enough to support the miners.
Another point is that miners will likely see increases in efficiency over time, so when the block subsidy is reduced it will have little effect on the ongoing profitability of the miners as they will be able to use this added efficiency to have lower electric costs.