I suppose the real difference is between short term and long term.
If you double the number of salesmen, you can increase your income right now. Firing all the salesmen would drop the income to zero.
If you double the number of developers, there is no difference during the following month or two. If you fire all the developers, you can still continue selling the product for a few months, maybe years.
As a manager, you may be tempted to increase the short-term profit, grab your bonus, and get promoted to somewhere else, so that someone else will have to deal with the long-term impact.
If you double the number of salesmen, you can increase your income right now. Firing all the salesmen would drop the income to zero.
If you double the number of developers, there is no difference during the following month or two. If you fire all the developers, you can still continue selling the product for a few months, maybe years.
As a manager, you may be tempted to increase the short-term profit, grab your bonus, and get promoted to somewhere else, so that someone else will have to deal with the long-term impact.