I am from India, but have lived in US for 7 years. So, trying to answer this based on my experience in both countries.
Because India has a lot of cheaters, especially towards foreigners. One reason for this might be that it is easy to recognize a foreigner in India than it is in US, because of its cosmopolitan nature.
There are cheaters in all countries, but the percentage of such people in India is quite a bit higher than you would find in US. So, even though it may be a little bit more expensive going through an agent, a client would still prefer it to avoid the headache.
PS: I am an Indian, living in India. I wish things were different. Sorry if I offended anybody's sentiments.