Earlier quoted context omitted.
H1B workers can, and routinely do, switch companies. Their new employer has only to file the paperwork to transfer their visa, so your assumptions about retaining H1B workers are not very accurate.
I've mentioned this elsewhere before, but I've had experiences at both ends of the H1B chain. In one workplace & location in the US: The H1B workers were...not very good. Adequate, and hard working, but not highly skilled and they were brought in mainly because the location didn't want to/couldn't pay wages good enough to hire skilled US-based talent. There the H1B workers were (in general) fearful and unwilling to c…
The former H1B workers probably were in the US as an onsite assignment or through a consultancy/contractor. Most Indian consultancies view people as warm bodies on the chair. Which is why you find people with fewer skills.
The latter workers are most likely people who relocated to the US for education or were hired from India from a US employer because of their skills.