The animation, which used to take three seconds, was a quick and easy way to leave the dungeon that saved players a lot of time they would otherwise spend running back all the way to beginning. It was/remains a nice feature (even now), but Blizzard decided to extend that cast time to five seconds.
Patch 1.1.0 made a lot of people upset for a variety of reasons, but that the portal time change felt like adding insult to injury. What made it worse is that when Blizzard discussed the changes in a post-patch livestream, the developer had this strange non-answer to offer, which somehow left us more confused.
Of course, the "justification" only made players think the increase was made to optimise engagement time, and perhaps because Blizzard was preparing to sell premium casting animations that would work better with the five second window.
During Friday's Campfire Chat livestream, however, game director Joe Shely (who made the original confusing statement) acknowledged that his explanation wasn't the best, and actually did provide a more reasonable breakdown of why this change was made.
According to Shely, the window was increased to prevent players from escaping tough fights. He also admitted that it was not the most elegant solution, as the team could've approached the problem from a different angle, such as allowing certain enemy tiers to cancel the casting animation immediately when they hit the player.
Nevertheless, the cast time is being reverted back to the original three seconds in Diablo 4's upcoming 1.1.1 patch, which is due next week. This is far from the only 1.1.0 change Blizzard backpedalled on, which is good.
In case you missed it, Blizzard is also working on a large number of improvements to horses that include the removal of certain cooldowns, making boosting more powerful, and fixing level geometry so horses don't get stuck on everything.