How can Apple Numbers increase its market share relative to Microsoft Excel?Why would Apple Numbers want to increase it's market share? Apple generally doesn't care about market share in any field; they care about mindshare and profit share, both of which they dominate in the hardware field. As far as Numbers/Pages/Keynote go, Apple is offering them for free. They don't want people buying a Mac and then being forced to go out and buy additional software to get basic functionality out of their computers. So they try to give a great out of box experience. They have no interest in competing with Microsoft in that field nor should they. They make no money from Numbers so why should they care if people use it?
Assuming they did want to spend money to increase market share of a free product they offer, which gains them nothing, they could promote it more heavily in the Mac App Store, push out TV ads and billboards. However, I suppose if they really wanted to push it they could just automatically have it installed on all Macs instead of just giving offering it as a free download. Once again though, why would they?