Follow the money
At the end of the day, whether the singles guys are better players or not doesn't amount to a hill of beans. The only thing that really matters is who is watching.
When it comes to which event to promote and put on television, what matters is which audience will spend the most money with the sponsors.
While the younger guys are probably better players - the older, "club" players likely have more disposable income.
Since the prize money is significantly less for doubles, sponsorship should cost less. And if (a big if) the audience has more money to spend with the sponsors, per capita, than a purely singles audience, a case could be made that doubles is a better investment for the sponsors than singles.