It's not that simple, because most companies don't perform inter-departmental cost accounting. A salesperson might seem to be very productive, while actually selling made-up solutions that are very cost-intensive to implement. To get a real number on how productive they are, you would need to measure:
([sum of sales * price] - [sum of solutions sold * implementation cost]) / compensation
or even:
customer price * weighted average of per-deal profit margin / total compensation
The cost to implement isn't added value. This kind of internal debiting would also change how management looks at IT. If they can solve the problem for less than the estimated cost by the salesperson, they're turning a profit. If they're taking longer due to "science fiction" products being sold, the blame lies squarely with sales. As it is now, salespeople are mainly incentivised for units sold and total price for deals made. You can be a rockstar salesperson while simultaneously mainly causing huge problems downstream.
at a very low level productivity is hard to measure because it's tacit and implicit rather than explicit. The reason why we can measure the productivity of a business is because it responds to price signals and you can put a literal number on what they put out.
You can try running some sort of market scheme within your company but at some point the trade-offs are bad and it adds too much complexity and creates strange incentives.
For software in particular if anything the opposite of your assumption is likely true. It adds a lot of value without necessarily being able to put a price tag on it. It's pretty hard to measure what wikipedia or vim is worth in terms of productivity as long as they're not charging, but that doesn't mean it's not worth anything.