Not sure. But they wanted to incentivize being in a guild or at least the same server for current content. If they made everything in the game cross realm-able then there would be no need for guilds because you could poach the best players from other groups across the world, along with there not a need to have paid server transfers. With this restriction it builds value and encourages others to make guilds or play with the community that they have (or need to rebuild) on their server.
you can never do current content tiers x-realm
if you could, guilds wouldn't be as they are now, an entire raiding group can be from different realms, and that is not what blizzard wants.
being able to do non-current tier raids x-realm, makes it easier to get the achis and such you are missing
You can do every OLD raid. They just don't want you to run to other servers to do current content. You're on your server for a reason, if you want to raid in other realm, they want you to buy a server transfer.
I'd imagine recruiting for a lot of guilds could get a lot tougher (easier for some). Imagine competing with every guild in your region :/
Recruiting for guilds might be tough. Filling raid spots wouldn't be. I have a bunch of people on my friends list I'd love to bring into my raid on those days I have a spot open, but can't because ToT can't be CRZ.
Not to mention the website openraid would be sooo much better if ToT could be CRZ.
This comes up pretty often now. While Blizzard does profit from server transfers, I think it's short-sighted to place that as the one and only reason. Normal/Heroic raids are one of the last areas of the game to promote server community. If you could do current content cross-realm, there would be little to no incentive to be in a guild, or even to stick it out at all with an organized raid at all. At the first sign of trouble, people would just jump ship and find a new group, since you could look across all recruitment for the game, not just those on your server.
I mean, if Blizzard were so incredibly concerned with maximizing server transfer profits, why introduce cross-realm tech at all, especially with the many complaints from CRZ?
Because Blizzard doesn't understand or have any way to predict what would happen with guilds if this were allowed. So rather than possibly break that it's left like it is for now. I predict that it only happens when cross-realm guilds are enabled (if that ever happens). Then there's no choice.