“We want to be transparent and communicate openly with our pro community, so we want them to know that the Mac Pro is a 2019 product. It’s not something for this year.”
In addition to transparency for pro customers, there’s also a larger fiscal reason behind it.“
We know that there’s a lot of customers today that are making purchase decisions on the iMac Pro and whether or not they should wait for the Mac Pro,” says Boger.This is why Apple wants to be as explicit as possible now, so that if institutional buyers or other large customers are waiting to spend budget on, say iMac Pros or other machines, they should pull the trigger without worry that a Mac Pro might appear late in the purchasing year.
Source: Apple’s 2019 Mac Pro will be shaped by workflows | TechCrunch