I'm sure people are studying them. But as GP said, antibiotic are lazy. A doctor would much rather prescribe an antibiotic than do the work to match the specific bacterial infection with the particular phage to deal with it.

And since antibiotics still work (for now), there's not all that much money in phage research. If we do get to the point where we "run out" of antibiotics due to bacterial resistance, I imagine phage research will become a lot more attractive as a destination for research funding.