Because Bandai wants to get in on that Iron Man action
I remember a crazy time, I think it might have been about ten years ago, when the name "Iron Man" was largely unknown outside the comic world. Stan Lee himself once described Iron Man as always being a b-list character, not on par with the likes of Spider-Man or the X-Men. And now, practically overnight, Iron Man is seemingly racing Batman and Spider-Man in terms of figure production.
If you think that Iron Man has had a lot of figures in recent years, you'd be right. Besides having multiple figure lines devoted to him in America (in addition to appearing every other wave in lines not devoted to him, such as Marvel Legends), he's really taken off overseas as well. He's had several figures in the Revoltech line and is getting a figma along with some other Avengers. Like Spider-Man, he's even had a nendoroid! Instead of focusing on where he's received a figure, maybe we should just look at where he hasn't. Square-Enix still hasn't added him to their Play Arts Kai line, for example. And Play Imaginative still hasn't announced a Super Alloy Iron Man despite it being the most intuitive selection for a Super Alloy figure.
All kidding aside, the S.H. Figuarts Iron Man may be that definitive Iron Man figure for everybody who hasn't picked one up. Well, that or the figma version. Personally, I'm satisfied with my current Iron Man providers and probably won't be switching over to this long-distance plan.