If you make it easier for those folks to switch, they will switch away from Infosys to a better job after spending a month or two working for cheap, as you say. If that happens a lot Infosys will stop bringing in new people since they mostly leave early but they already paid for their immigration costs which add up. The employees also will be less inclined to work 80 hrs a week for Infosys to rake in the profits.

If they want to retain people, Infosys will have to increase their salaries to close to market rate by charging the client more, which means the client is less likely to hire from Infosys. Either way it's a win.