Why does my partner always tell me how attractive other men are?

Question sums it up really. I know I'm a pretty good looking/attractive guy so it doesn't bother me too much. I just find it...odd.

My girlfriend is constantly telling me how attractive other men are. I don't just mean the occasional 'he's good looking/handsome' kind of passing comment either. I mean constantly telling me how attractive other men are and what is attractive about them, sometimes almost in a fawning kind of way. It can be in any scenario as well, on tv, in the street, in a story she recounts to me, a friend or someone she knows etc...

I normally just bat the comments off, but sometimes they do make me feel uncomfortable depending on what it is. Even if I don't say anything though, she continues to labour the point and I just can't wrap my head around why.

Unfortunately this weekend I did bite at it, and I feel kinda bad for that now. To give context, a few weeks back she told me about a guy her sister hooks up with when she's here who is handsome. OK, no problem with that. But then she really went into detail about it - how and why he's so handsome, how he's buffed up which helps him etc. I didn't really know what to say so I didn't say anything, but she continued to talk about it until she talked herself out. I let that slide until we actually bumped into the guy on the street on Saturday. Afterwards, she started on this crazy-long tangent about his looks again. I actually said that I didn't think he was as good looking as she made out (really, you would have thought this guy was some sort of Greek God by the way she spoke). Her response was 'oh no, he IS handsome...maybe you didn't think so because you didn't see him with his shirt off' and proceeded to talk about it further. That did cause me to say something (not angrily may I add), and I wish that hadn't been the case in hindsight. I just find fawning over real people that you know to be very different to a celebrity or someone on the TV who aren't very 'real' in that sense.

Maybe there is some level of underlying insecurity on my part which I am willing to acknowledge. After all, this guy looked NOTHING like me (dark skin and kinda buffed up, I'm pale skinned and more lean). I just don't know if even the most confident man on earth could listen to a partner speak in that way almost daily and not find it a little discomforting. I suppose for me it's less that I find feelings of jealousy, just kinda annoying...it's just like, why tell me about it so much? What do you want me to say? Sometimes it feels like she almost wants a reaction from me.

I should just caveat this by saying I'm fully aware that my girlfriend, like me, has eyes and the book doesn't stop at me. I also don't find all comments in that regard make me feel uncomfortable. But fawning/thirsty comments about real life people are a bit much for me. By contrast, I almost never tell my girlfriend when I find other women attractive because I would think it's a bit disrespectful to her, and also just doesn't feel like a natural thing for me to say to her. Of course I have eyes, just like her, but she doesn't need to know that. It can't do her any good, only make her look inwards on herself which I wouldn't want her to do because I think she's amazing as she is.

So what is the logic behind it? Is she telling me this stuff because she thinks she can speak freely to me as her partner? Do others do this so often? Or could there be something else at play?