There’s a practical maximum amount of thrust to get from a single turboprop engine; to meet performance requirements in the event of the failure of one engine, that puts a practical upper limit on the size of two engine turboprops. Four engine turboprops would likely not be competitive with modern two engine jets, except on the shortest of legs.

Turboprops also fly lower, meaning they’re much more affected by en route weather that turbojets can often climb over. (Low and mid twenties [thousands of feet] is where much of the uncomfortable weather is. Storms that rise into the mid-30s are diverted around by most airplanes.)

Turboprops have their place, but so do jets in air carrier ops.

It looks like the future is a bit of a mashup of a turboprop and turbofan. Check out the efficiency of the Pratt and Whitney geared turbofans. On the A220-100 fuel burn (~3,800 pph) is comparable to a CRJ-900 with 35 more seats in a dual class configuration. That’s quite a leap. I’ll see if I can find someone to compare it to a B717 fuel burn, it’s the same number of seats.