Those are optimized to create the strongest possible shockwave however (aside from nuclear weapons maybe), and generally come in very large sizes, that cause huge explosions to begin with.
A fragmentation bomb of similar size still has a similar or greater danger zone.
Of course there are some other factors to consider: fragmentation will be hampered in confined spaces, while it actually makes concussive force more potent, so, aside from clearing out mines and obstacles thermobaric or purely concussive weapons are used mostly inside buildings or against cave complexes and such.
Another advantage to them is predictability. Purely explosive weapons have a very well defined danger zone, so you can use them closer to your own troops.>inb4 Janny gets mad for OT