They'll continue to use them until a design change is required. The whole reason they still sell the (mostly) original Raspberry Pi board is because there are systems, processes, or fleets still using them. Also when companies build products and internal solutions around the Pis.

When people like you and me buy these boards to play with or build into our projects, we are subsidizing all of the foundations design, education, outreach, activities. What people here seem to be forgetting is that these things take money and instead of spending time fundraising (a huge cost and time sink for most non-profits), they decided to tap into the maker and computer geek communities, as well as industry. They also do quite a lot of education and outreach themselves. The Raspberry Pi foundation's mission is to increase technical literacy worldwide by making and selling very low-cost yet reasonably high-performance computers. From a practical standpoint, I don't get the complaint (I mean, how does that personally harm them in any way?). There have been a lot of commenters in this post basically complaining that there are too many Raspberry Pis. I'm not entirely sure what you're saying, but it sounds like you're arguing against their strategy of having multiple variants of the Raspberry Pi for sale at the same time?

Raspberry zero octoprint