Why does my boyfriend adds girls he doesn't know on Facebook?

He doesn't do it very often, nor do I think he would ever cheat on me, but it makes me feel a bit uncomfortable that I can see he would go out of his way to add somebody who he clearly doesn't know/has no mutual friends with/can only see pictures of (selfies/provocative photos). To me it is fairly obvious that he adds these people to see their pictures because they are attractive, and I think a lot of men do this too. I don't feel like I should say anything to him because I guess he's not done anything wrong, he always tells me how much he loves me, would never hurt me, treats me well etc. I know that men will look at pictures of hot girls just for amusement etc, but the thought of him seeing a random girl on Facebook and seeing/liking her pictures so much that it compels him to add them to see more doesn't make me feel good. I do think he is committed to me, so it's not a question of does he still love me/going to cheat on me... I'm more just wondering WHY guys do this? I've made the decision not to bring it up with him, no point, but every time it springs back into my mind it gets me a bit pissed off. I'd just like to know from a guy's perspective why men still do this even if they are being satisfied every day, twice a day (!) most days, are in a relationship and their girlfriend/wife/partner can plainly see who they're adding on Facebook and that it's not hard to tell they don't know them.
Why does my boyfriend adds girls he doesn't know on Facebook?
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