Because historically the old mac pro was a more than a 6000 dollar toy that only the rich and studios purchase. Apple is basically pissing on all of their old mac pro fans who are getting priced out by this update.
I think the "this is for studios" argument is just an excuse to make up for the fact that Apple completely missed the mark with this new refresh's price point. If Apple _really_ wanted to create a flagship desktop to appeal to studios, they would have not used the mac pro's name, they would have created a new brand for the SKU to reflect that its target audience is different from that of the mac pro.
I think the "this is for studios" argument is just an excuse to make up for the fact that Apple completely missed the mark with this new refresh's price point. If Apple _really_ wanted to create a flagship desktop to appeal to studios, they would have not used the mac pro's name, they would have created a new brand for the SKU to reflect that its target audience is different from that of the mac pro.