there are rules in place that allow people to port mods even if the creators aren't around. it's common courtesy to ask people for permission to use their works, and even if they're not around, there are rules in place that give you the go-ahead anyway as long as you make the effort to reach out. portlegs are what happens when people don't make the effort to get permission.
you're very blind to the genuine talent and effort people put into their mods if that's what you have to say about them. samus is a good mod, one of my favourites, but it's easily one of the most complicated and i'm not going to die on the hill that people should strive to match that. even shine himself has said he doesn't want to. quality is 100% subjective but you're really limiting your own experiences if you're going to write off 99% of the mods released as bad or not worth your time because they're not as intricate or elaborate as samus. you'd surprise yourself. i definitely have.
mods are absolutely art. besides the fact that 90% of the work that goes into most character mods are the sprites (which i really hope i don't need to explain), every part of the creative process of modding is...creative. you're creating, putting things from your mind onto the canvas or file. that's art. creating is art. art is creating. and the notion that just because it's a fangame and not technically legal is horrible. there's a ton of work, time, passion and effort that's gone into srb2, and to dismiss it because it's just a fangame is just disrespectful.
disrespect as a whole is my main point of grievance here. you could go out of your way to ask for permission to port something, and those who do generally get a positive response, and sometimes even the go-ahead. they ask because they respect the art and the artist enough to give them the choice of how they would like their art to be treated, and in this case also preserved for what are functionally their original intentions. portlegs are ports without any trace of respect, because there's no input from the original artist. they're content to be consumed at that point. they're things to play, just like you described them. there's no art in them.