Why would a man not tell me he’s bi?

I thought I was talking to a straight man who said he thought I’d be open to something serious but he really just wanted sex… and he disrespected me when I basically didn’t want to and I told him in the beginning I wasn’t really ready for anything..

But I found out through social media and the dating app that he’s bi… he talks to non binary/ trans individuals… and I can’t understand why he wouldn’t tell me that in the beginning when wanting sex… I felt a bit devastated… because he posed as a true masculine man who I really wanted to be with
Why would a man not tell me he’s bi?
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