Lots of cases, the throat is destroyed by a tumor, or the surgery to remove the tumor. These people may have to wear these for weeks for recovery or permanently. (permanent patients will likely have a similar port in their belly to pump Ensure into their stomach)

The most common cause is smoking of course. I've seen half a dozen people smoke through their trach.

A temporary tracheostomy can be a trauma procedure - it's a way of securing the airway by directly ventilating into the trachea via the tracheostomy tube. When there is an injury or severe swelling in the neck, there is a risk of the airway blocking off and also a risk of debris including blood going into the windpipe from the mouth/throat as they're joined together. People can suffocate or even effectively drown from stuff going into the airways (aspiration). So a temporary trachestomy bypasses the upper airway and a balloon helps stop stuff going down.

A temporary tracheostomy can also be used prior to and after surgery for cancer if basic structures of the deep neck are intact. The cancer or swelling from treatment like radiotherapy can compromise the airway temporarily. In that situation once everything is healed, there is still a safe separation between the airway and the food pipe and the tracheostomy can be taken out.

A permanent tracheostomy is usually after cancer, after a total laryngectomy (the voice box is removed) or a laryngopharyngectomy (the voice box and the food pipe is removed). The food pipe can be reconnected but it's not safe to reconnect it to the airway so there is a permanent connection to the skin made instead.

Tracheostomy literally means opening into the trachea. The trachea is the lower airway, and a stoma is an artificially created opening.