To anyone who takes "hardware issues" as "the Wii U is too slow for us to develop for", you're wrong. That's not the problem. Games that pushed the 360 and PS3 were de-rezzed and released on the Wii, which had a much larger gulf of processing power than the Wii U vs the XBone and PS4.
The problem is architecture. The XBone and PS4 are now running x86 processors designed by AMD, the Wii U is running a recent iteration of the IBM PowerPC processor. In layman's terms, Microsoft and Sony's consoles now speak the same language as PCs (including Macs), the Wii U still speaks the last generation's language, which is now almost entirely associated with mobile technology (RISC->ARM, et cetera).
Bethesda will now have a very, very easy time making triple-platform releases (so the two console releases should see no more bugs than the PC release, in theory. At the very least, it'll be a lot less than last gen's stuff)... but putting those games on the Wii U would require a rebuild almost from the ground up, for a much smaller audience than any one of the other three platforms. On top of that, switching architecture pretty much guarantees a repeat of the bugs they encountered as a result of that last gen. So they're not going to bother doing that with any of their major open-world games. Those things are a lot of work.
**edit**
This is also why they're waiting on the next generation's release to put anything else out. At this point, it makes sense to either develop for the PS3, 360 and Wii U... or the PS4, Xbone, and PC. Trying to cross over from one side to the other would be reliving the coding nightmare that was the past decade or so. When one has a viable option to choose between RISC or x86, only an idiot chooses both.
Additionally, this is why backwards compatibility for the PS4 and Xbone would be all but impossible. Same issue the PS3 ran into with PS2 compatibility... they had to actually integrate a PS2's processor into the thing to make it work (still glad I have one of those), which was ridiculously expensive to manufacture. Everyone learned this lesson from Sony's attempt: when you switch CPU architecture, axe your back catalog. Hell, in the Xbone's case, the CPU is not only a different architecture than the 360's, it's also running a much lower clock speed, just on more than twice as many cores. Even emulation would be impossible it its case.
The problem is architecture. The XBone and PS4 are now running x86 processors designed by AMD, the Wii U is running a recent iteration of the IBM PowerPC processor. In layman's terms, Microsoft and Sony's consoles now speak the same language as PCs (including Macs), the Wii U still speaks the last generation's language, which is now almost entirely associated with mobile technology (RISC->ARM, et cetera).
Bethesda will now have a very, very easy time making triple-platform releases (so the two console releases should see no more bugs than the PC release, in theory. At the very least, it'll be a lot less than last gen's stuff)... but putting those games on the Wii U would require a rebuild almost from the ground up, for a much smaller audience than any one of the other three platforms. On top of that, switching architecture pretty much guarantees a repeat of the bugs they encountered as a result of that last gen. So they're not going to bother doing that with any of their major open-world games. Those things are a lot of work.
**edit**
This is also why they're waiting on the next generation's release to put anything else out. At this point, it makes sense to either develop for the PS3, 360 and Wii U... or the PS4, Xbone, and PC. Trying to cross over from one side to the other would be reliving the coding nightmare that was the past decade or so. When one has a viable option to choose between RISC or x86, only an idiot chooses both.
Additionally, this is why backwards compatibility for the PS4 and Xbone would be all but impossible. Same issue the PS3 ran into with PS2 compatibility... they had to actually integrate a PS2's processor into the thing to make it work (still glad I have one of those), which was ridiculously expensive to manufacture. Everyone learned this lesson from Sony's attempt: when you switch CPU architecture, axe your back catalog. Hell, in the Xbone's case, the CPU is not only a different architecture than the 360's, it's also running a much lower clock speed, just on more than twice as many cores. Even emulation would be impossible it its case.