I forgot to add this in to my earlier post, so I'll just add it here before I have to head out.
I don't think it was a requirement for them to stick with the old style. In fact, using something new, not quite the same, I feel was the better move, as it helps to show that this incarnation is its own identity.
I have heard of continuations of old shows that keep the old style. Like they are making The Jungle Movie for Hey Arnold and they are making a special for Rocko's Modern Life. But the thing is, like I just mentioned, these are continuations, not reboots.
And Ducktales 2017 is a reboot, not a continuation.
Using the old style with it would have felt strange. Especially since it does not share the same continuity as the show and is more similar to the comics. If it used the old style from the cartoon, people might have been thrown off and confused. Using a new style helps prevent confusion and further solidifies the whole "yes this Ducktales but not the one that you remember". It's a good visual representation to show that what you are watching is not the old 90s Ducktales that used to air on Disney Afternoon.
I can understand not liking the new style. But I can't really agree that the reboot should adhere to the old style when it's not supposed to be a continuation of the old show; it's supposed to be something different.