I certainly don't know what the incentive is, but there's a ton of scammers using bots, scripts to auto-text crap to any random phone number they can in order to find which are in use, and then the real crap starts to pour in.
For myself, that meant tons of nude images and bloody animal picture sent via MMS until I cut the SIM card. I don't know if they just got sick pleasure out of it or what because it's not like they wanted my bank account or other personal info, just fishing for a response to send disturbing images. A fetish?