Probably because his insurance or taxes went up and they need more money to cover the difference.
Escrow account at a mortgage company is a small fund that you pay into every month that pays your property taxes and your homeowners insurance. The mortgage company does this so they can be sure those items are paid and the house doesnt get destroyed by a natural disaster with no insurance or get sold at a sheriff's sale because of non-payment of taxes.
The payment on the escrow account can go up and down depending on whether ot not there is enough money to cover those items. If there is extra after those are paid, most mortgage companies will send you a check, and lower the payment a bit.