Why do some people's Facebook pages not have a friend request button?

I’ve twice encountered this, and one person had no idea why her page had no friend request button.

I am not very good with social media. In fact, when I had an active email account, I used to just send a message and ask the recipient to send me an email. because I’ve had so much difficulty with other media.

Is this something they designated in privacy settings or something? You’d think a person could just ignore or delete unwanted requests. You never know who might want to contact or reconnect, and that’s why I don’t ‘get’ this option, if it is indeed an option.