Android promotion: pay per install

I tried looking for ways to promote Android apps. It was hard. Why companies aren't saying: we're doing Pay-Per-Install campaigns? (alternative names include: Cost-Per-Install, CPI, Cost-Per-Action, CPA)

Here's a list of pay-per-install for Android I've found so far (on going work, please correct me if there's something wrong here):

• AppBrain - Free apps only, Minimum bid: 0.20$, minimal daily budget: 25$, minimal campaign budget: 100$. See more details here. No SDK integration required,
• TapJoy - Pay-per-install plus optional pay-per-action (which probably cost much more). Minimum bid: 0.10$ for rewarded install. SDK integration required. Does not accept PayPal.
• Flurry AppCircle - Free & paid apps. Minimum bid: 0.75$
• Everbadge - Free & paid apps. Minimum bid: 0.15$. SDK integration required,
• AppRedeem - Free & paid apps. Minimum bid: 0.50$ (paid apps), 0.15$ (free apps)
• PlayMobs - Minimum bid: 0.10$ for rewarded install. No SDK integration required.

Possible Pay Per Install, not sure:

• HeyZap - ???
• RadiumOne - ???
• W3I - ???
• Appia - ???
• Zedge - ???

References:

• https://groups.google.com/forum/#!msg/android-discuss/tlYilbiPhDc/nxKsnze59tEJ
• User comment: updated Everbadge minimum bid.