Default applications are an endless no-win situation for distro developers.
No matter what applications are selected, there will always be a segment of the population who wants something different. If they decide to switch from alacritty to kitty, there will be other posts recommending the switch back in the other direction.
The alacritty package uses ~6MB of disk space and the kitty package uses ~18MB of disk space so having both installed shouldn't be a tremendous hardship.
If you prefer kitty, use it. It shouldn't matter if it is the default or not.