I'm not really sure why. Probably the same reason they don't consider mobile games real games? This is a vast medium so it's not really possible to define what a video game is anymore.
I think we can thank the Wii and the mobile platform for having sooooo many titles that can be considered shovelware. So many games are out there that are just too short, awful to look at, or just downright terrible to play. It's obvious someone was just out to make a quick buck and it seems like folks think that's what indie developers are. They don't want to invest in a huge studio, but want to make that quick buck off of a trending subject.
I didn't realize there was a sect in the gaming community that didn't consider indie games as games. It could be rooted from either a bad experience with an indie game or an underlying insecurity that leads to a forced elitism.
This could also just be a case of following what's popular. Same as there are people who only go to the theater to experience just the massive, AAA-budget blockbusters, there are a lot of gamers who are only interested in massive, AAA-budget franchises. It's a shame, because much like some of the best movies ever created are smaller-budget indie flicks, some of the best video games ever crafted were done so with small budgets by indie teams.
At this point, if someone won't give indie games a chance simply because they're indie games then that's their own loss. I'm not going to try to convince them why the dungeon crawling of Severed is unique or how Oxenfree and Inside successfully craft compelling, original stories or that Journey is a truly emotional experience. The people who want to play indie games are playing them and that's good enough for me.
What does indie really mean? Is it studio size? Budget? Is it just something people feel like calling a game if it looks cheap? The term literally comes from the word independent, which means that they don't have a publisher, so if we go by that definition there are actually a whole lot of indies that aren't really indies.
If people want to ignore some of the best experiences that gaming has to offer due to some arbitrary reason then they are idiots that don't actually love the medium.
This is an unfortunate reality of games and people consuming it. While I don't necessarily keep an eye out for the next big indie game, I don't abhor it, either.
I embrace these smaller games since they usually drive innovation forward, and have some unique gameplay elements that AAA games won't even dare to try.
I guess some people just think that all games must have cinematics, and be big-budget affairs, which is erroneous. Open your eyes and you'll see a whole new way of playing games.
Not every game needs to have the shiniest graphics and allow you to kill your enemies 1,294,830 different ways.
Why don't some gamers treat indie games as real games? I honestly have no clue, and they're missing out on some great gaming experiences if so.
With most indie games being made by smaller teams, generally being less complex endeavors, which ultimately sell for a lower price, I can see how many gamers would consider them as "not real games."
I, however, love indie titles. I think it's great that, even with a (usually) minimal budget and workforce, a unique idea can be crafted into a wonderful gaming experience.