Lender transfers mortgage

[Account Closed]

I have an existing mortgage and the lender turned it over to another mortgage company to service the loan.  Apparently this is their routine practice with mortgages for rental properties.  I don't care either way, but I am just wondering how this is profitable to the new lender?  Are they piecing it up and selling it as part of mortgage-backed securities?  Do those still exist?

Asking to satisfy my curiosity only.