Remaking RE1, which they'd done several years ago, and still have all the assets to isn't super simple, but its rerendering and then other touches.
For RE2 and 3, they're basically starting from scratch, they can't reuse the old code for a full HD remake, they can't reuse the old backgrounds because now looking back even if they were HD they'd still be a bit bare bones compared to todays pre-render detail levels, so even a straight port in Hd would require editing. So all that would take a year or 2, then theres all the staff, redoing all the music, re-recording all the voices (probably in at least 2 languages), it'd get expensive real quick.
Finally it'd have to sell a few hundred thousand to make back what they put into it, and chances are it wouldn't sell that, a few thousand easily, maybe even as high as 100k, but I don't imagine much more than that, not without a lot of advertising, which then costs evenmore money.
nintendo remakes, they touched up controls and fixed some bugs, but texture wise its mostly just good upscales, and so it doesn't look amazing, the Majoras mask changes for models are awesome looking, but textures still look grainy as ever.
WW lends itself well to rescaling due to its size, even running the original in Dolphin at Hd resolutions it looks amazing, not as good as the remake, but quite close texture wise. They put a lot of work into it, but like almost all HD remakes, its not that much compared to what the consumer really wants.