His internal polling tells him that he'll attract voters from both parties and it'll be an even 3-way split. Maybe this is true? Or maybe it's just so he can look himself in the mirror.
Nonetheless, he's scaring the crap out of Democrats and the media because he resembles the old Democratic Party before they went bash*t crazy with intersectional SJW far-left socialism and if he ran, it would be most likely be President Trump that benefits. That's why Trump is egging him on, media figures are in a dead panic, and Leftists are calling for Starbucks boycotts until Schultz promises not to run.
Schultz will attract potential Trump voters in blue states that would go democrat anyway, with a chance, if Shultz wins, of taking electoral votes that would have been democrat.