Why's my giveaway total so low?

Bundle games.

It's a bundle games...

http://www.steamgifts.com/forum/Ihcl4/how-were-planning-to-fix-bundle-keys-and-contributor-values-option-1-revised

Max bundle contribution = Non-bundled contribution * 0.2 + $30

So if your non-bundled contribution is $0, you can give away $30 ($0 0.2 + $30) in bundled games before you are capped.
If your non-bundled contribution is $100, you can give away $50 ($100 0.2 + $30) in bundled games before you are capped.
...
If your non-bundled contribution is $4000, you can give away $830 ($4000 * 0.2+$30) in bundled games before you are capped.

This system is in place so that people cannot just give away bundled games and farm contribution. If you want your bundled contribution cap to increase, you must also give away non-bundled games.

This question just keeps on returning :O

Got it. Thanks everybody.