I mean, people buy, so it's worth doing that. In the end there is demand from people to play old games in more modern technological glory. If it wouldn't be interesting to many people, people wouldn't do it.
And in fact, I very much enjoyed some remakes myself.
There is the matter of graphics, but also the matter of quality of life and accessiblity that progress every year. I love some old games, but very commonly the controls irk me or the fact that I can't do some things. I had to unplug my monitor to play old Battle Realms for example, because it would throw a fit if you had more than one monitor. The remake fixed this.
I also believe that people very much enjoyed the Resident Evil remakes.