People have been asking for this a lot actually.
Too many people on these mega servers have been burned, often more than once. That’s actually a big reason why the mega servers exist because people do not want to pay money and move their guilds (which moving the guilds is also a risk you tend to lose people just doing that - a lot of guilds die from moving but this doesn’t get talked about) and then have to move again.
With that being said the transferring back is almost guaranteed to kill the realm that people move to so this is also bad.
So I don’t know what to say, but you’re right. It’s a huge issue. Group moves are the best way to ensure part of the community stays together but also that’s an issue and often creates a faction imbalance on the new servers.