But why can’t I transfer from a pvp realm to a pve realm? As I said in headline, if I missed this question I apologize.
You can now go from pve to pvp, but all the gewd pvp realms are locked 
Free transfers may not be on offer from PVP to PVE but you should be able to purchase a transfer to PVE if you are interested. They lifted most restrictions on 21 June.
Oh dear…I tried all of that but thanks. It’s not available.
Blizz generally does not allow PvP toons to transfer to PvE realms (and vice versa) in Classic. Their reasoning is that the differences between the two realm types could be exploited in ways that either disrupt server economies or negatively affect the experience for other players on the servers.
That said, they seem to have relaxed that rule with regards to the “free transfers” currently being offered to reduce queue times on highly populated servers. Earlier this evening I was able to transfer all of my toons on Grobbulus ( a PvP server) to Old Blanchy, a PvE server.