Because anyone who understands how bitcoin works, and understands what transaction batching is, will be thoroughly underwhelmed by this. Individual users like myself have been using transaction batching for literally years. If we can do it, then there is absolutely zero reason that arguably the largest and most valuable bitcoin related company in the world couldn't also do it years ago. In reality, the fact that it took them this long to finally implement it should really be a source of embarrassment for them, not something to announce to the world as if you are making some massive progressive strides forward.

They have announced it with great fanfare, and a bunch of newbies who don't understand any better will think "Oooohhh, they are saving me some fees, isn't that amazing! How great are Coinbase!", whilst anyone who understands what is going on will just roll their eyes.