Oftentimes, foreign citizens working in the US are not able to freely participate in the job market. If they can't freely move from job to job (as US workers can), then they will be paid less money. If they want to be in the US badly enough, this will still be their best option. Everyone wins except the local worker who is now competing with an indentured servant.

[0] Indentured Servant is probably an exaggeration: but google sure has a lot of hits: http://lmgtfy.com/?q=h1b+indentured+servant