Retina-class displays aren't just for photo editing.I don't do any photo editing so I don't need the 218 PPI. At 27" even 115 PPI 4K is good enough. But I still wouldn't buy the 27" Studio Display when I can buy the LG 32U990A-S UltraFine evo 6K Nano IPS 224 PPI for $1300 (MSRP is $2K).
For many of us, the 218 ppi is essential for text work.
I have a 163 ppi side-by-side with my 218 ppi, and I find it noticeably less fatiguing to view text with the 218 ppi because the 163 ppi looks slightly fuzzy by comparison. So my eye is always searching for focus on the 163 ppi but can never quite find it.