(Via Stephen Hackett.)
Sad, but not a surprise: there’s very little space in the market for desktop email clients.
Most people use webmail for their personal email and big-corporate mail systems such as Outlook with Exchange at work. Relatively few people want to use desktop IMAP clients instead of webmail or corporate systems, and the built-in Windows Live Mail and Mac Mail clients are good enough for nearly all of them.
There’s room for one or two niche clients such as Sparrow, but only if they’re radically different from the system clients. Thunderbird isn’t. (And I can’t speak for its recent years, but for most of its history, it’s been good on Windows but buggy as hell on Macs.)
It’s also worth considering the cynical angle: Mozilla can’t make money with Thunderbird the way they can with Firefox (web search placement and affiliate fees). The undertone of their post is “You all weren’t helping with Thunderbird enough, and we can’t justify doing it ourselves.”