It wasn't necessarily even a bad call at the time. Apple was originally founded as a partnership, and Mr. Wayne was worried that he would personally be on the hook for foolish debts incurred by Steve Jobs.
Its an interesting story that people always are interested in because all of these What If? questions basically assume that they would have a positive outcome if they made one single decision.
Sitting on 10% for decades might've made Ronald Wayne a multimillionare but only in exchange for not being able to sell any of the stock until literally today. For some people it's unfortunately not practical to wait it out.
Oh, and not to mention there were plenty of points in Apples history where it's future was not so certain.