If you're curious to learn more, there's plenty that come up in a simple Google search.
> It's pretty hard to imagine how more developers wouldn't lower salaries though
This is the textbook definition of the lump of labor fallacy.
The answer isn't always somewhere in the middle. If someone tries to convince you that the Earth is flat or that climate change isn't happening, I would hope that you will lend more credence to the experts instead of believing the answer is somewhere in the middle.
H1Bs also distort the market because getting a sponsored visa is a huge deal for a lot of people. Yes they may make slightly less than market but they have the ability to come to the US legally and have all of the paperwork filled by the hiring company (and legal support).
As another commenter mentioned, they're also locked into your company and can't quit without leaving the country. Another win for hiring managers.
None of this is good for local talent though. It's absolutely naive to believe that the supply of labor has no impact on its cost.
So you're saying that you willfully violated federal law by bringing in guest workers for cost reasons alone.
It's pretty hard to imagine how more developers wouldn't lower salaries though. I say this as someone who's done a lot of hiring. It's really hard to find good people and they can command a premium (fair market wage). Being able to hire H1Bs helps hiring managers but I don't think it helps developer salaries at all.