All though a remaster, the general public don't hate remasters. Also don't forget most people don't write positive things, they write negative things so there is always a vocal minority, Look at most election around the world. The majority voter stays silent and Polls mean nothing.
I also bet the main reason for these sales is Mario Sunshine. Gamecube sales were not great and a lot of people just did not buy the game either as it was a radical change to the N64 mario and people kind of went WTF did Nintendo do. Since then the game has grown on people and the userbase has also grown on Nintendo systems, so if they want to play Sinshine it is now an expensive game on Gamecube. This is the cheapest way to play it so it will sell well.
Can it really be called a remaster?
It is true that people mostly write negative instead of positive. But again looking at the other thread mostly was positive comments about the collection and was here in the forum.
I was excited about the collection when I heard (sure I didn't pay attention to the 3D so was even expecting the older 2D games as well, but that is on me), but when their selection of games was limited to a point to not include last gen and also not the sequel on the same gen, the full price and lack of real improvements on the games I got pretty disappointed.
I don't think most of the people buying this are old timer that have played Mario 64 or Sunshine because of the "lack of sales" during that gen, though. But I'm more talking about the VGC behavior instead of the market itself, on the market most of the collections have done fairly well (sure not as well as Mario will do, but that is also because originally they didn't do as well as Mario anyway). But in VGC we have seem many times this.
I just call anything on a next gen system a remaster, but I guess its technically slightly enhanced ports.
Personally I got no issue with any ports unless they do what Crapcom do, so naturally I will be excited if I liked those games when I was younger. My biggest beef is probably games coming out then 12 months later they do a game of the year editions, which implies they really were not ready to launch the game in my eyes.
I think the other reason people used to hate on ports was because it wasn't enhanced (like this collection with some effort) in the past, where as lately devs put a bit of effort in to make it better. I think real Remasters, especially going from say PS3 to PS5 for AAA games will be fantastic seeing them use ray tracing and better graphics. It will add to the experience and make those games even better.