Here's why:

* Plasma is an ionized gas, meaning the atoms have been stripped of some or all of their electrons. This creates a sea of free electrons and ions.

* Stars are incredibly hot, causing the atoms within them to move with such high energy that their electrons are easily knocked off.

* This ionized state gives plasma unique properties, like being highly conductive and easily influenced by magnetic fields.

While stars contain some gas, the vast majority of their matter exists as plasma due to the immense temperatures and pressures within them.