Almost everything in law expires, because law is to be reasonable, and not having an expiry is generally unreasonable.
For example: When you do due diligence while buying a house or a company, collections are one of the things you need to check. How far back do you need to check the archives? It would be unreasonable to require you to go all the way back. So there's a limit, and it's set so high that it doesn't matter for everyday life, yet low enough that the lawyers and notaries who check the archives can do their job practically.
Where I live, a collection expires after 30 years, but it may be much less, there are usually other relevant rules. A single-digit number of years is not unusual in case of collections against a person.
(BTW, you're confusing revenue with either profit or cash on hand. Profit is revenue minus costs, and the costs are usually a much bigger than the profit.)