Been doing it for so long, I forgot why I started.
But I've been gardening just about as soon as I could walk, and most years since (except years I was at sea). There's nothing like fresh vegetables... the feeling of independence that you get from providing part of your own sustenance, the joy of watching things grow, and eating something secure in the knowledge of what is - and is not - in your food. It is a nurturing pastime, as opposed to other less constructive activities which might otherwise occupy my time.
It is also fun to explore new vegetables, new varieties, new techniques - to play citizen scientist. To find just the right varieties, with just the right flavor, and pick them at just the right time. To watch the garden get a little bit better every year, and to share the bounty with friends & family. During peak harvest, those home cooked meals are to die for.
And for me, a large part of my gardening is to grow & share seeds with others.
I'm blessed with a DW who loves gardening as much as I do... I doubt I would be half as involved as I am now, if we did not share that time together. Love is sitting in front of the TV together, shelling edamame.