Skyfury is one of the Freshstart realms, which is why it’s only recieving transfers from another free start realm. If you’re not on a fresh start realm, can’t transfer there. But yes Venoxis and Morgraine are at the population where the server is too big, and thus, Blizzard probably fears they’ll become megasevers.
While not accurate data, ironforge.pro is a good way to see what the population of each roughly is. However, Ironforge.pro only tracks those who raided, it does not count anyone who logged on and didn’t raid.
Data from Feb 1st-Feb 7th
Venoxis- 22060
Morgraine - 16,112
Even though these servers are large, I bet they were the picked destination realms because the servers that could transfer to them were so small in number that their transfer wouldn’t make much of a difference to overall pop and server stability. Now I really don’t know why these servers would be given as a destination if they’re not receiving character transfers, if I had to guess, these servers used to be open to transfers and then people took those transfers, Blizzard shut off the transfers to those servers, and simply forgot to update the list. But I’m honestly not too sure. /shrug.