At vero eos et accusamus et iusto odio dignissimos ducimus qui blanditiis praesentium voluptatum deleniti atque corrupti quos dolores et quas molestias excepturi sint occaecati cupiditate non provident, similique sunt in culpa qui officia deserunt mollitia animi, id est laborum et dolorum fuga.
Et harum quidem rerum facilis est et expedita distinctio. Nam libero tempore, cum soluta nobis est eligendi optio cumque nihil impedit quo minus id quod maxime placeat facere possimus, omnis voluptas assumenda est, omnis dolor repellendus.
Itaque earum rerum hic tenetur a sapiente delectus, ut aut reiciendis voluptatibus maiores alias consequatur aut perferendis doloribus asperiores repellat.
You earn them by getting medals.
And buying them would kind of remove the goal of getting to that point where you can have multiple titles.
Smart cents are a way of measuring the quality of your work (generally, the higher quality your answer is, the more smart cents you get). Therefore, by buying smart cents and earning titles like "honorary professor of mathematics" without having solved 3,000 math problems, new users won't know the difference and they will think that you are truly a math expert, while the reality is that you really aren't. So buying smart cents, really, reduces incentive to solve more problems and replenish your supply of smart cents in order to gain more titles.
Does that make any sense? @nasa7 I know you mentioned that you still have to have the required amount of medals, but if you have the required amount of medals, then you should also have the same amount of smart cents, given that you haven't bought any titles. If you have bought titles, then you just have to keep answering questions to earn the titles. This system keeps you in a question-answering cycle, so eventually, you can have enough smart cents to buy yourself another title. Then ultimately, your smartscore will be on the rise.
For all those reasons, I think the system is fine just the way it is :) Feel free to grab some more opinions from others.