>new employer has to go through the entire process of getting them a new H1 visa.

this is not true, saying this as a person on h1 who changed jobs easily.

when talking about indentured servants you are probably referring to small Indian IT bodyshops, that keep people on low wages due to them being on a very long green card queue, but this has nothing to do with H1 per se. These people do not work in big tech