Over the years, I've worked with a number of products. Some of them start out easy to use and stay easy to use. Some of them started out easy and then got harder because they added a bunch of features and didn't take time to clean up the GUI when integrating them or - worse - there's a totally different GUI for the add-on and it's way different from the one I got used to. And then there are the ones that didn't add features, but they did ruin the GUI and chose to double down on the crap instead of rolling back to what I was comfortable with.
A change in GUI is like inviting the competition in if the product doesn't have a "revert" button. I can see wanting to have a new look for marketing and sales purposes, but the daily users of the product likely have lots of memories attached to what they're doing and how they're doing it and changing everything makes them feel useless. Replaceable. Unimportant. Judged by the makers of the product and found wanting. And that makes it easier to burn a bridge and move on.