Apple does not make their own 4K displays.
Where once an architectural office never seemed to have enough desk space to layout drawings, today most architects workflow has migrated to the computer. That has driven the need for larger and larger monitors. Though monitor sizes have topped out between 27-inches to 30-inches, the resolution is going higher and higher allowing you to see far more on one screen than ever before.
Even thought Apple has been selling Retina displays on their MacBook Pro line for a couple of years now, they only recently introduced a high resolution screen on the iMac. If you are not in the market for the iMac with Retina 5K display, but need more pixels then check out Peter Cohen 4K Mac Display Roundup at iMore.