Trending @Capgemini; Why Do IT guys changes to frequently while working for consulting firms?

Why do techies change jobs every two years when working for consulting companies such as Capgemini, TCS, Infosys etc when compared to Product based companies like JPMC, CITI, etc etc..

I joined Capgemini for 14L 4 years back and today my CTC is 16.5L, my friend who is working for JPMC joined for 13.5L 4 years back and his current CTC is 24L. Just trying to figure out