You are absolutely right, having a mentor isn't a criteria for success, you can become very successful without having a role model or any one you look up to. Achieving success is all about dedication and consistency to you goals and ambitions. As a matter of fact having a mentor without having a drive or prospect would take you no where. Some people are of the opinion that having a mentor isn't necessary and believing in yourself and working hard is the only thing that matters, it's not entirely correct but it actually makes a lot of sense.
One funny thing about this mentorship is that you can do everything in your mentor way and still not make it in life. There is something about life, it's not about bed of roses, success has nothing to even do if you work everyday, you can work every day and still not be successful if life want to be unfair to you. You can be at the top of your game and life can bring you down under some seconds and there is nothing you can do or your mentor can do at that point.
True that, one of the reason is that people tend to keep the most essential secret to their student. It is rare to find a mentor that will expose all his knowledge, most just give people a basic guide and let them figure out the rest. This is the reason why even if we have mentors, it is hard for us to reach what they had achieved unless they will really guide us step by step and tell us their secret formula to success.
Having a successful life is about been able to make what you plan for at the right opportunity, every successful person that you see today saw an opportunity even with the hard work, without it life becomes nothing, with all the plans you make and no opportunities, it is nothing. This is why the idea of mentorship is nothing to me in my opinion but I like seeing and hearing successful people as my own way of motivation but another man's life can't be my way to the top.
It is all about decision making and the timing of how these decisions are executed. Even with the best strategy if the execution misses the opportunity, all the effort will be in vain.