Here are few reasons why sewer lines fail.
Clogs – You should only flush waste and toilet paper down your toilets. Flushing things such as diapers, baby wipes, paper towels, etc., can clog up your sewer pipes and create buildups.
Soil shifts – Things such as heavy rain, flooding, drought, freezing temperatures, and other environmental changes can cause the soil around your sewer lines to shift. This movement could crack or break your sewer lines.
Tree roots – If tree roots find their way inside your sewer line using cracks or joints, they can clog up your pipes and slow down your drains.
Older pipes – Homes built with older pipes such as terracotta and cast iron are reaching the end of their life-use.