Every time I've seen this it's because of inefficient and wasteful use of 10/8 internally. Like, not every tiny site or thing needs a /24. Once the wasteful use becomes entrenched as a practice, it would be very labor intensive and time-consuming to go on a renumbering plan. As compared to the effort to just use 11/8.

And then ultimately because of refusal to get over the technical hurdle of using IPv6 for internal management.