Men and lying about watching pornography

Why is it that men think they have to lie about doing this. I would rather him just flat out say hey when I'm hanging out in the garage for long periods of time I'm watching porn. Instead when I ask him why he had a weird look on his face when I walked in the garage to throw something away he was hiding in a corner pretending to be looking in his tool box. He got so upset bc the first time I caught him I beat around the bush on asking him what he was doing. He then proceeded to tell me have I touched myself in this garage yeah I told him look I know men do it just a fact of life and that is ok it doesn't bother me( because we don't have any issues in the bedroom) but then he gat upset and tells me well you don't need to make comments like that bc It's not a regular habit. Need some help guidance here he is not an easy person to talk to about these things I feel he gets more upset when I bring it up. I mean we are suppose to be honest with our partners right? Idk I don't want to be the wife that checks up on him all the time but when I go out there to talk to him or see if he wants to watch a movie or just general questions I walk in and he is in the corner of the garage