Convenience.
I don't always have power up front without an extension cord and I don't want to have to rely on battery power if possible.
My mixer (that I run my DI into) has phantom power so it could work well for my situation.
I do run my Hartke pedal on phantom power when I use it and it is just way easy to only use one mic cable and be done.
I did find
this one from L.R. Baggs, but I don't necessarily need a preamp.
