Without the sales effort, there is little or no commerce. Without commerce, there is little or no growth, only stagnation. That high is the fruit of their labor, the reward they reap for the due diligence they've paid the client. The joy of making a sale is so intense for me that I often find myself selling for my clients. Most of the time, such incentive is regarded quite positively as being indispensable.
Passion is clearly what is expressed in someone's exuberance and enthusiasm.
When this exuberance is muffled, inhibited, and burned out, a bit of one's passion dies. Salespeople are expected to outdo themselves time and again. If they sold 10,000 widgets in January, they should be able to sell 11,000 in February or January next year or both. Instead of management focusing on improving customer relations and helping salespeople grow their proficiencies in other areas, many managers focus on numbers and statistics. This type of superficial focus is what destroys passion and energy.