Why is it hard to find available mentors?

I recall a conversation I had a while ago with a younger friend just starting her career. She being a hardworking person started working on her certifications right from college, running her part-time masters program while working at her first job less than a year after her first degree. She attends trainings and conferences occasionally to get the exposure her job requires despite her very demanding job. She is deliberate at being successful at her career. But, there was always one question that troubled her, which she once asked me; “Why is it so hard to find a mentor who is willing and available to put me through this career path?” Before I could answer her, she unleashed more mind-pondering questions; “Who is your mentor? Who do you meet when you are at a crossroads regarding career decisions?” I did manage to give her some reassuring answers that allayed her fears and frustration. But till date, her first question still lingers on my mind; Is it really hard to find AVAILABLE and genuinely interested mentors? I refuse to believe that the problem is that no one has the expertise to guide younger people. Should my friend just continue to put her best in all she does, learning from her mistakes; hoping that she’ll get it right one day?