Investors are tripping over themselves to invest in messaging startups again.

Eric, Tom and I hear Sequoia Capital and other VCs have been considering putting another round into productivity service Slack. We also hear Slack, which launched last year, has been seeking a valuation of as much as $1 billion, citing as a comparable the $1.2 billion Microsoft paid for Yammer. And then of course there is Snapchat in the midst of raising at $10 billion.

Messaging is a big deal. This summer I wrote about how messaging services are going to become interfaces to everything: media, businesses, brands and more. 

But messaging is not a good business. The list of messaging companies that have become big standalone businesses is short. Really short. They usually sell (Yammer, Hipchat, MessageMe), sometimes for hefty sums (WhatsApp). Or messaging is used as an engagement driver for companies that have different revenue streams, like ads (Facebook, Twitter, Pinterest); stickers, games and other in-app purchases (Line, Tencent); or increasingly, subscriptions (Evernote, Path).