First of all, I want to say that this a very good question even though it relates to a subject most people fail to understand it's concept. I've had the same thoughts as you every time I see people like random pictures which often do not translate into a meaningful message. I think most people like picture because of the reason you stated in your narration, and probably because social media behavior has made it like a must do behavior. Personally, i don't like random pictures because am familiar with the poster or because I simply choose to indulge in social media sentiments. Call me old fashioned, but I like to think that socializing isn't just about fun, it's also about expressing our inner self. And since social media brings people from all around the world in one place, i feel every post should make or show some kind of sense since we are looking to engage people in getting to know us. I also know that social media is a platform designed for showcasing arts exchanging ideas and passing knowledgeable information to one and another. So if I come across a certain picture that doesn't look good or pass any form of meaningful message, i tend to move on to the next. Overall, i think the core basis and idea behind social media has long been buried. People just choose to interact and behave in different ways that suits their personality.