Uh... not to be all captain obvious here but...There aren't that many more coins to mine. There's a fixed number and that's it.

There's going to come a point where they're going to have to do something about coin scarcity. As it is, the rewards for mining are not like it was years ago. You have a very slim chance of "winning" the transaction race, especially when you consider all the BTC mining arrays/farms that dominate the field.

Furthermore, it's not the best technology for crypto - there are several that are faster and more secure than BTC.