1. They probably don’t trust local Indian companies enough to sub-contract as much.
Boeing builds AH64 Airframes in India, Everyone from Ford, Audi, Hyundai, Honda, Toyota, has Mfg plants that is part of their global supply chains.
3. Even a lot of the software work has a lot of bugs, like the software in the 737-max.
Look up TCS, as it stands - it is the most valuable IT company. All major banks, Auto company, IT company, Insurance company utilizes Indian Software companies. Even the so called "bug" for 737max that you insinuate was attributed to HCL, that has a revenue of 8.63 billion dollars, to put that in context of this forum; that is close to twice of the entire revenue of the entire IT industry of entire nation of Pakistan.