Because the media hypes it to be one of the best things in the world and, if you?re not in a relationship, you?re missing out (e.g. Valentine?s Day, a marketing scam for reasons I can?t be bothered to get into now). Also, hormones.
But, based on my observations of my friends? and other people?s relationships, it?s mainly a more powerful form of companionship, to the point that just being around them makes you feel good inside.
And, btw, no, it?s not ?so easy to get laid nowadays?. For many people, the only way they can laid is with a partner, since casual sex isn?t for everyone. Just like relationships, I guess. And even they can vary on a scale of seriousness.
I mean, no offence, guy, but it?s a bit like asking ?What?s the point of having friends? Eventually you?ll just drift apart from when you move cities, go to university, whatever, so if anything, it?s more for convenience.? Boyfriends and girlfriends are, essentially, a higher level of friend; someone who you can talk to about intimate issues and be intimate with (as well as feeling you?ve fulfilled your biological imperative by finally satisfying your sexual frustration into the man/woman you love).