Like all other types of outsourcing, this one is also driven by the price differential for skilled labor between the US and India:

In Kerala's churches, memorial and thanksgiving prayers conducted for local residents are said for a donation of 40 rupees (90 cents), whereas a prayer request from the United States typically comes with $5, the Indian priests say.

Bishop Sebastian Adayanthrath, the auxiliary bishop of the Ernakulam-Angamaly diocese in Cochin, a port town in Kerala, said his diocese received an average of 350 Mass intentions a month from overseas. Most were passed to needy priests.
In Kerala, where priests earn $45 a month, the money is a welcome supplement, Bishop Adayanthrath said.

This means a priest can double his salary by saying 9 Masses for special intentions, assuming that they collect all the surplus for their work (unlikely), and that the parish isn't skimming any off the top for "administrative overhead"

Interestingly, prayer outsourcing has been going on for some time. Most of the current outsourcing of services happened after the telecom glut slashed the prices of calls and data transmissions to India, thus reducing the transaction costs involved. However, sending masses abroad is "several decades old" and was justified in the beginning, when there were plenty of US priests, as "a way for rich churches short on priests to share and support smaller churches in poorer parts of the world."

Finally, as with other kinds of outsourcing, Indian service providers defend this practice by saying that their quality is as high as that of any worker in the US or Europe:

The Rev. Paul Thelakkat, a Cochin-based spokesman for the Synod of Bishops of the Syro-Malabar Church, said, "The prayer is heartfelt, and every prayer is treated as the same whether it is paid for in dollars, euros or in rupees."

No word on whether prayers without any money attached are also equally heartfelt. Thanks to Marginal Revolution for reminding me of the story, which is actually 3 months old.