In our case they are milking the past - and doing a good job of it. My current consulting customer has some kind of cloud mainframe agreement with IBM as the result of an acquisition. I don't know the specifics, but I'm integrating data off of it. It's not easy to work with and a lot of tools don't support it. My initial suggestion was migrating to AWS RDS, but there are too many existing integration points and business rules coded to make this cost effective. The cost of migration is something like 20x the annual platform cost.

Edit: I should also point out that they provide stellar support and a great transition from on site hardware to their cloud service. They have always been great to work with - at an appropriately high price.