It may be a regional thing because I find my MA business to have higher retention. In most cases they are locked in for the majority of the year and cant move anyway, and the low income ones dont think they can move either (forget what they'e been told) Also they are on a zero premium plan there are very few plans they will consider switching to. "You mean I actually have to PAY??" Also the rate increases on MA premiums are much lower than Med Supps. I think all these are factors.
I'm speaking of them staying with one carrier. My MA clients are with me for a long time, but not with the same carrier.
As the market matures and carriers finally stick with plan designs, the migrating of clients from one plan/carrier to another will decrease and then the value of a book with one specific carrier will increase in value.