I thought it was probably due to increase in premiums on the Homeowners' Insurance policy which is required by the lender, so that they would not incur the loss in the event that house (on which the lender has a lien on until it is fully paid for) is destroyed by a fire or some other damage. Many borrowers contribute to an escrow account (maintained by the lender on the borrower's behalf) which is used to pay the insurance premiums and also property taxes. When the insurance company decides to increase the premiums (which happened to me last year), the lender would notify the borrower to contribute more to their escrow account.
I am not sure if that's what happened in this case, but it does make sense to me.