1. I'm neither pro nor anti, I am a realist though, those who own the rights to recordings need to generate revenue from their assets.
2. Although those albums/singles may have sold millions or even tens of millions 30 years ago, they are no longer the popular music of today. The rights holders have two choices: A. They could just reissue the original, with no remastering, aimed at those who want to buy again what they bought 30 years ago or B. Remaster it to appeal to a younger demographic. Even though "A" is much cheaper to produce, it's uneconomical, not enough people buy them to make it worthwhile. B. Is economically worthwhile, which is why they do it!
3. Of course there are modifications, if there weren't any modifications it wouldn't be a remaster, it would be a reissue of an existing master!
You're just going round in circles now, pretty much all of these points have already been dealt with!
G