It's almost always been that way, even in the early days of EPs and LPs, the stuff that sold most gets reissued. And in this new climate where the labels are cautious about sales, putting out something "safe" is far easier to get up and down the channels than something obscure or that did not sell a lot in an earlier incarnation.
Many of us are jaded collectors who are now wanting the obscure and neglected, but I will say I do appreciate many of these sets for bringing whole bodies of work together under one cover and one mastering (often). And for new jazz fans these sets can be great, they can get a lot of material quickly and easily and with little duplication of what they may have started with.