The people making these decisions think customers respond better if the UI gets a "visual refresh" from time to time, and they're probably right.
It's human nature to judge by superficial attributes. If you have a perfectly good UI but it never changes, it gives people the feeling that your software is stagnant and out of date.
It's inconvenient for the user, but it catches the user's attention and makes them think about the software. Essentially it boosts brand awareness. It's the same reason that they change the design on a box of granola bars and write "new look, same great taste!" on it.
It also costs engineering / designer labor. And there's a danger of replacing the old design with a newer one that doesn't work as well. The people making these decisions probably know that but think it's worth the cost anyway.
It's human nature to judge by superficial attributes. If you have a perfectly good UI but it never changes, it gives people the feeling that your software is stagnant and out of date.
It's inconvenient for the user, but it catches the user's attention and makes them think about the software. Essentially it boosts brand awareness. It's the same reason that they change the design on a box of granola bars and write "new look, same great taste!" on it.
It also costs engineering / designer labor. And there's a danger of replacing the old design with a newer one that doesn't work as well. The people making these decisions probably know that but think it's worth the cost anyway.