Particularly for throws that are targeted at beginners, I feel the yo-yo should come with everything the player needs to start the hobby and that means enough string to last them a little while.
I realize that these companies and vendors sell string too and they want those sales, but in the long run creating new throwers is what will benefit those companies the most and therefore they should try to avoid losing people losing because the beginner gets a yoyo, quickly ruins the string, and then just says “to heck with this.”