SE didn't put it off, they have more important things to do for THIS UPDATE, like fixing the game and adding content. Server merging will come AFTER they do what's more important.

Merging servers right now will do nothing but allow more people to play together on a broken game still. They are thinking, any business would do the same thing:

"Do we merge servers now and hold off on content and fixing the game so they can all play together?"

"Do we fix the game, add content THEN bring people together right after?"

What's the more logical decision? Merging the servers would help just as much as fixing, but the priority is with fixing the game. No one wants to play a broken game, even if you have 7,200 people to choose from, your game is still broken and it'll be even more apparent with thousands of others.

Remember how the game used to be, the more people = the slower the server responded which means the laggier the interface became, if they fixed that issue then a merge after a major update will be worth the wait.