Why would a guy dump me due to “lack of mutual attraction” when he asked me to be his girlfriend a few days before?

I went on three dates with a guy with my MeetUp group in less than three weeks. On the third date, he asked me to be his girlfriend. I was taken aback by all of this being that we had only known each other for less than a month and each date was 2-3 hours each. I told him that I was not ready for that level of commitment yet and wanted to get to know him more. Three days later, he dumps me due to “lack of mutual attraction” and it “doesn’t feel right”.
Why would a guy dump me due to “lack of mutual attraction” when he asked me to be his girlfriend a few days before?
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