I also noticed this change almost immediately, as it makes the hero feel very clunky. I actually cannot overstate how much of a difference this makes to the feel of the hero, despite the fact that I wasn't even that mentally aware of cancelling the animation before, as it was just subconscious.
This is especially noticeable when casting burrow after jumping from a building, as you are locked into the animation until you hit the floor. This feels especially bad against knock-up heroes.
I am assuming the ability to cancel the animation was removed due to a bug that allowed for the hero to become invisible (and semi-invincible due to lack of a proper hitbox) by spam cancelling the ability.
The animation for burrow would play, where Mo dives into the floor, but the animation would not reset when you cancelled the cast. This would leave your model under the ground, without using burrow.
The bug was in the game for an incredibly long time, especially considering that it was actually quite egregious/abusable, but I don't think that removing the ability to cancel the spell entirely is the way to go about fixing it.
I'm pretty sure the bug could've been resolved by fixing the way that the animation looped when spamming & cancelling the burrow spell.
I am praying that this is just a temporary fix, and not the final solution, as it really does feel awful. I have my doubts, though, because as I understand it, burrow is technically 2/3(?) spells under the hood. Cancelling the animation as you would in, say, Dota 2, may have never been intended at all.
