All the times I've either patched Winrar or ignored the 40 day subscription nagging did not matter for their bottom line at all.
You individually? No. But RARLAB aren't saps; the "40-day limit"(TM) transforms their software from nagware into something valuable the user is "getting away with". If one or two stray consumers happen to purchase a license based off of that, then excellent. The real kicker, though, is that a culture where everyone uses WinRAR for creating and extracting archives is one where they can push a ton of business licenses – one of the main reasons e.g. Microsoft will often provide Office to universities at steep discounts. By using WinRAR, you act as a brick in the wall of WinRAR's (thankfully waning) hegemony, even just by giving it word-of-mouth or not using competing software.
They want you to feel like you're getting more value than you are out of a product that is near-strictly inferior to free and open-source software with a public domain compression algorithm like 7-Zip. This has been common knowledge for over a decade.