I don't even understand why you're being downvoted

People on this site don't like it when you buy a sequel and get its predecessor for the same price as a new game sequel by itself? What?

It sold 2 million on two separate platforms that had a much larger install base on the Wii U at the time of its release.

I mean, 760k on an install base of 7-8 million is actually quite a high penetration rate.

To add to what pook said, Bay may have been a new IP, but it most certainly wasn't the only one of its kind on the systems.
Devil May Cry had already introduced gamers to that kind of frantic combo-based hack&slash action, so Bay 1 had an easier time selling to those systems because the fan base for a similar style of game was already there to fall back on.

Yet they only sold 2M across the two, and it took quite a while to do it.

Meanwhile, Wii U had almost literally nothing like Bayonetta 2 on it, and far fewer to sell to, yet it eclipsed the week 1 sales of the original, and although it slowed down since then due to not having as many to sell to, it's still selling so long after its initial release, and is going to eventually hit 900K, if not 1M, by the time the Wii U is done.

To top that off, it still managed to get those sales despite active boycott campaigns against it early in its life, from haters claiming to be fans, who slammed the game solely due to their allegiance to other systems and the fact that it wasn't a multiplat.
Despite the fact that Nintendo saved it, when no one else out of the other big names wanted to fund it.

No matter how you spin this, Butt, Bay 2 is an under-dog success story.

Just pointing out the figures reported on a certain web site.