Most of them weren't, but some were. If all you were doing was looking at screens of text, a long persistence phosphor could be desirable[0].

I've got one that is inside an Apple II monitor. Can confirm, the image looks very flicker-free, but has pretty bad ghosting if you're looking at anything that scrolls. It looks cool but is pretty rough to do any work on. The other green CRTs I have are barely more persistent than a regular black and white TV, and I've never heard of a long persistence color monitor.

[0] - http://www.trs-80.org/soft-view-crt.html