I think it's a bit more complicated than saying your goal should be your strongest motivator or simply pinning your bank statement on the wall, that is a method that is subjective, if it works for you.. great, it could even be an idea that may also inspire others. However, people turn to motivational 'Gurus' (I really hate that word especially when it is self professed) when maybe they do not have that someone to say something positive around them, that someone to say the words they want to hear to remind them to keep going when things look bleak. Some people have started out highly motivated without even reading a book or audio but over time things have not worked out and may have become depressed and they seek to get that motivation back.
Let's be honest a lot of motivational speakers out there are charlatans, they use carefully crafted words and tones, promises, blueprints, funnels, freebies and offers with some of the best marketing techniques you can find to lure you in to take as much money as they can from you, but it is a business and there is a demand for it and it works for some people and doesn't for others just like any other business.
I'll be honest I do not buy these things but I do wonder around youtube to watch and listen from time to time, some are good and some are just plain rubbish and as mentioned it is a 'Time Thief' but once again it's all subjective.
Sorry I could not answer the original question but I was compelled to respond with my opinion and it's my first post.. Yay!