Salesfolk tend to be the most rational economic actors you can find. If a salesperson can make a reasonable living by just picking up the phone and signing somebody up, they're never going to do anything else. Why should they?

If you don't have an extensive sales cycle, there is zero reason why you need to pay commission.

If you want rainmakers, you've got to set up a sales incentive program that demands it, and then brutally winnow out those who don't make the grade. Otherwise, pay them a base salary and then a fixed bonus based on the entire group making quota. Brutal winnowing is still encouraged in this situation, to cut out the losers who aren't closing.