Sir Brennen
Legend
My first thought as well. I suppose it depends on whether WotC outright owns the art - i.e., the artist sold them the picture, so now it's WotC's to do with as they please - or if they simply sold first publication rights*, which means WotC would need to ask permission to reuse the art in a different context. Even if it were the latter, I'd think it'd still be cheaper as the artist doesn't have to produce anything new. Though of course, there's the argument that it deprives another (or even the same) artist a chance to sell a new piece.Honestly my only concern is in artist compensation. reusing art is a good way to cut costs.
*I don't even know if this is a thing with regard to artwork, as it is with written works, particularly things like short stories. There may be other contractual bits which entitle the artist to compensation for reuse.
Otherwise, I'm okay with it in this instance. The "new to me" is a big factor, and even if I did still play M:tG, as @Umbran said, being able to see a better version of the tiny card artwork is a bonus.
However, I'm not particularly fond of D&D art being re-used in D&D products. If you're going to give me a new edition, I want new pictures of Monsters in the Manual, not the same ones from the previous edition.