Initially, Kubrick planned narration for the film, so that it would make sense. But once he saw the visual impact along with the temporary classical music (the movie also had an original score that Kubrick dumped), Kubrick decided to make the movie mysterious and puzzling. And most importantly, like with all his films, he wanted it to make money.
It made money, but after struggling at first it was a big success. People still quote the movie and talk about it fifty years later. If somebody wants to make sense of the story, they can. It’s easy to do now with the Internet.
It’s too bad that people who so easily dismiss the movie don’t know what they’re dismissing. Back in 1968 on the big screen with the format Kubrick used it was breathtaking and nothing like it up until that time. It took another 10 years for Star Wars to come out with a similar effect but with a much easier story to understand. Many film makers were influenced by 2001.
And 2001 was lampooned extensively!