Those are very probably businesses which have a legal "business presence" in California... that is, they have an actual physical office, warehouse, or other real property here.
In those situations, the business is subject to California regulations and taxes, and must collect and remit California sales tax for any product sold to California residents. This applies even if the products are shipped to the buyer from outside California.
The same rules generally apply in other states (at least, those which collect sales tax at all... if I recall correctly there are one or two which do not).