The point of that entire category is to complete the game as quickly as possible. Just because a category exists, though, does not make it representative of all speedruns. Those that say it defeats the purpose of speedruns doesn't really understand the community, or how these speedruns evolve over time. Just because it took 2 minutes to watch the speedrun doesn't mean it took 2 minutes to complete. Anyone who is familiar with Kryssstal's work with LttP knows that she puts in hours of dedication to optimize her runs, testing tricks over and over until she figures out how to do them properly, and consistently.
But your whole complaint about it would make sense if categories did not exist. LttP Any% is no longer a very popular category, and categories that outright ban some of the glitches pop up and take over.
Glitches, in general, take time to learn and perfect. A part of the speedrunning community is dedicated to finding these glitches, seeing if they're doable by human hands, and then practicing them. It's incredibly fascinating how these games have evolved over time, especially popular favorites like Ocarina of Time, where tricks are still found 15 years after the game released.
It's kind of funny; any time a speedrunning topic gets brought up on a website like Kotaku, there's always a deluge of comments complaining that glitches "aren't fair." The community laughs at these comments more than anything, because it just proves how many don't understand the work that goes into these games.