Charging 1.01x the expected ad revenue wouldn't cover the cost of implementing the no-ad option. Even 2x might be in break-even territory when you include extra support costs and the like (one person on the phone because they bought no-ads and got ads due to a mishap somewhere wipes out the profit from a lot of no-ad sales).

There's also the funny issue where people who can afford to pay extra for the no-ads option are exactly the people that advertisers want to show ads to. If the no-ads option is $5, then you're left selling ads with a target market of people who can't afford or don't want to spend $5, and that ends up driving down your ad revenue. A large gap between the expected ad revenue and the price of the no-ad option helps mitigate this effect.