The question gets asked frequently enough. I think my reasons are obvious enough, but it's interesting to think over them once in a while. Incidentally, I always insist that I dance 'Argentine social tango', which seems to suggest something a bit more straightforward than what's generally seen on TV or the stage. 'Social tango', that is, as against 'unsociable tango'...
Because there's always something awesome about holding an other close, even for the duration of a dance, about that physical proximity, so close that you might just feel the other's heartbeat. The late Ricardo Vidort joked, to reassure reluctant close-embracers, 'Hold your partner close! It is not for life, it's just for a dance!' - suggesting that you don't have to take too seriously what you do in a dance, that a dance is of no real consequence. But perhaps he was being just a little disingenuous. Are life and dance really so remote and opposite as he suggests? '...just for a dance!' As if!
I've heard he also said that 'Tango es una terapia que hace liberar el alma'. So, why tango? Because 'tango is a therapy that liberates the soul'.
The fact is that tango 'allows' us to be close to an other and to enjoy that closeness, and I've come to believe that it's one of the really good human creations. Absorbed into the music 'self' and 'other' cease to mean much for a while, as we move into the unknown, joyfully stepping out without the slightest idea what comes next, or where we're going, or how it will end. This temporary abandoning of the daily need to be a 'self' is where tango can be so liberating. One of the consequences might be that little laugh of pleasure at the end of a good tango: what was that about, where were we? Was that a dance or... was that life?
Being close to someone else is a responsibility too. You shouldn't step carelessly into that intimacy. If you get the balance between dance and life right, you can be carried away and brought back renewed. If you get it wrong, you step into a mess. We need a bit of control to keep life and dance in a balance that we can trust. To be that close means that perhaps we need to be able to rely on a certain distance, a slight restraint. That restraint is partly created by social convention, by the setup of the milonga, and it's also partly internal: yes, we need to remember that this is a dance, it isn't life. In part it's that social formality that gives us the freedom to lose ourselves in an other, and in the music.
I hope I can quote something Tango en el Cielo wrote recently as a comment to my post on 'Dreaming again...' It seems very passionate and clear, and it seems too good to leave at the end of a series of comments. 'I like the formality of the traditional BsAs milongas. The cabeceo system is the best one I know for getting to dance with the partners you want to dance with. I like music to be arranged in tandas so I can choose the right partner for the right music. I like to be in the company of people who respect the music, who care about it, and dance with attention to it. I like to share the floor with people who are respectful of my space and are trying not to bump and kick me. I like to dance with men who have taken care over their grooming and personal hygiene. I like a bit of decorum, a sense of occasion.'
There's always debate about how far we copy the customs of Buenos Aires, customs that grew up far away, and way before any of us were born, and we need to think about these things. But in the end it might just be that those customs still work best to give us the best experience we can have from that balance of life and dance we call tango. Perhaps, after all, we're not really so different from those people far away, and way before we were born.