if transaction fee increases to such extent, no small investors will show interest to buy it
It is much worse - it means that small investors cannot sell and get the Bitcoin out without the miners' stealing your profits as fees
I don't think they steal money from small investors
. It's what they deserve received cause if there are no Bitcoin miner your transaction will stuck forever, they have to spend a lot of money to invest in mining Bitcoin so this small amount is not a big problem, although the fee has increased a lot till last year but the price of Bitcoin has increased too so don't worry about it.