Money. ACIV is consistently voted peoples favorite AC. I mean you're a pirate and the ship combat is so addicting. I don't blame them. People buy up these remasters (no judgement, I'll likely buy as well).
I'll say if someone hasn't played Rogue, it certainly scratches the itch.
I completed that game 100% and I can say it's not worth it. Missions and Ship battles were exciting at first, but ended up being the same 3-4 missions repeated over and over, and the same battles over and over. The black suit was cool tho