@zverik maps.me/OM is just as popular. But that is not the point, the question is if spending the money on something provides a reasonable return/value for the money spent. And if you look it that way, spending money on anything except iD maintenance is literally pointless.
And given that there is a fixed pot of money, spending it on anything outside of what gives the best bang for the buck, actively damages the project.
@simon regarding the "fixed pot", that's an attitude I cannot support. If we're talking about OSMF, it's far from fixed, though OSMF makes it look so. In development in general, "a return for money spent" is not how you get new things. Like, no company besides Cloudmade and MapZen innovated in OSM on their own money. Because R&D doesn't bring money. Is spending on it pointless? Well, if your goal is to make more money, then yes. Is the goal of OSMF to earn money?