From SlashGear:

If a significant name like Facebook jumped onboard, though, that could prove a major draw to webOS. Something certainly sufficient to get HP thinking about whether its own phones and/or tablets might make sense. webOS struggled for the large part because there was no single reason why it was better than Android or iOS: no one point of appeal that HP could build a promotional campaign around. Facebook’s 800m users would certainly be an instant audience.

Facebook’s IPO, webOS and the Perfect Social Phone - SlashGear