Why isn't iphoto 11 available?

I believe you may have to have Mavericks installed.

http://support.apple.com/kb/HT4411

babowa is correct; the version of iPhoto now available in the Mac App Store requires OS X 10.9 Mavericks. If you cannot or do not wish to upgrade your system to Mavericks, you'll need to buy a copy of iLife '11 on disk. Apple no longer sells it but you can still find copies through some resellers, Amazon for instance:

http://www.amazon.com/Apple-MC623Z-A-iLife-VERSION/dp/B003XKRZES

Regards.

or ebay:

http://www.ebay.com/bhp/ilife-11