I'm not sure what you mean by paying less than it's worth. If people do the HITs, it's worth it to them (assuming they have some knowledge of the pay rate, either after having tried some of a batch or seeing a time estimate in a survey). And if people don't do the HITs, they don't get done.
By "less than it's worth," I mean much less than you could expect to hire someone to do the work for you in a more traditional manner.
The selling points of crowdsourcing are:
1. It's fast
2. It's cheap
This comes with a major downside of having to deal with serious quality control issues. If you were planning to start a project via crowdsourcing, the benefits would have to outweigh that -- and so you see even would-be decent requesters pushing the limits on how low they can pay while still getting the work done on time.
Unfortunately people are desperate enough to reward those using this strategy.