The best Indian engineers aren't working at these body shops, instead it's the bottom of the barrel and all of them are looking to either get promoted quickly or get out just as fast. As a result it's a revolving door of "resources" (urgh corp speak) that have to constantly be brought up to speed.
This is largely why most large enterprises operate on a bit of a seesaw w.r.t outsourcing.
They have in-house people do the thing, it's expensive and some new exec that just got hired or promoted tries to score a quick win outsourcing stuff.
So that continues for 2 years until exec gets their bonuses and leaves but now everything is a huge mess, business functions are paralyzed by outsourcing etc. Some new exec that was brought in to take the fall gets thrown out despite none of this being their fault.
New expensive exec is hired to fix everything, they hire a new in-house team, usually at inflated rates because you need to offer a premium to clean up Infosys/TechM messes. Everything starts looking good again after 18-24 months but the exec that fought for and protected the in-house team is now surplus to requirements and on the way out.
Cycle then repeats ad infinitum.