[Terr_]

To offer another possibility, with a cynical motive:

1. We have an established user-base.

2. Our product and our competitors' products have a similar interface, so we might lose our lead if people start switching.

3. If we abruptly change our UI, they will have no choice but to learn the new one, either because they're too-invested or because they aren't the ones making purchasing decisions and it is mandated by an employer.

4. Once accustomed, the difference we created becomes a barrier to keep our customers captive and away from the competition's products.