Bad bearings, abuse, just plain bad luck, improper maintenance and/or service.
Old age Frozen or misaligned pulley
A pulley on a Husqvarna can break due to several factors, including excessive wear and tear from prolonged use, improper alignment, or overloading beyond its designed capacity. Additionally, debris or foreign objects caught in the pulley system can cause it to fail. Lack of maintenance, such as insufficient lubrication, can also contribute to pulley damage. Regular inspections and adherence to manufacturer guidelines can help prevent such issues.
If you pry up on the pulley with a bar on each side of it and while keeping pressure on the pulley, hit the end of the shaft that the pulley is on with a brass mallet, the pulley will usually break free.
Age or damage from a failed pulley.
It will eventually wear out and break.
The idler pulley has nothing to do with the brakes. If the idler pulley is bad it could throw or break a belt, and then your engine will stop.
You have to purchase a special pulley puller from Dodge, other wise you will break the pulley when you try to pull it off.
You don't
Bearing seized on the pump.
This is called a sudden release of tension or force. The force that was once supporting the load is no longer present, causing the pulley to break and fall to the floor.
The bearing gets old and starts to heat up. The pulley fatigues... It's all just part of stuff wearing out.
Lack of attention (maintenance) causes break downs.