Why do guys not seem to appreciate compliments that much? See discription please?

I give compliments to guys quite often, not meaning anything by it other than I like their clothes or think their hair is cool or something else. But they always seem not so genuine in their thank you, and always just walk away. Like do guys do this when they have a girlfriend? Or do they not know how to respond? Should I just stop complimenting guys? Because it always feels so awkward afterward when they give the "ah, thanks" and walk away. I'm not saying every guy says that, but a lot of them don't seem to appreciate it
Why do guys not seem to appreciate compliments that much? See discription please?
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