[nitrogen]

Your "servicing" and "note" on a mortgage are two different things. The servicing right is who gets to interact with you and charge you money, but the owner of the note actually gets the money in the end (minus servicing costs). Those can be transferred independently, so you may keep sending checks to one place, but the actual owner may change over time.

One reason to sell a mortgage is to get the money back. Instead of making money slowly over 30 years, you get some fraction of that as a lump sum plus your principal is returned. Some investors want the steady payout for more, others want fast turnover for less.