Why do men, who are only interested in casually hooking up, get upset when women cancel?

I’ve been seeing a guy for about 2 years now. We meet up and hook up several times throughout the year (he lives in another state). I canceled our last meet up and he ends our casual link up. He was clearly upset even though he denied it. Why is he getting upset when I cancel but also states he doesn’t want a relationship.
Why do men, who are only interested in casually hooking up, get upset when women cancel?
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