Thom Brooks offers some answers here (via Leiter Reports).

He suggests three answers to why we publish –

1. Journal articles as a seal of approval

2. Journal articles as an academic job qualification

3. Journal articles as academic brand awareness

The post is worth reading, in part because the most obvious (or perhaps hopeful) reason – that we should publish because we have something to say, to contribute – is there, but only masked by other things…