Actually, someone or an entity does have to sponsor a non-citizen. You cannot stay in the US without a sponsor visa (a US citizen, a company, a university), otherwise, you would have the whole world show up at the US borders without regard for sponsorship.
As for Microsoft, Google, Amazon, those jobs are very limited. With the H1 visa, it is temporary, it is hard to get and US immigration doesn’t give them out like candy, it doesn’t lead to citizenship and, at any time, that worker can be replaced by a US citizen. As for Green cards, the waits are often after the expiration date of the visa.
As a non-issue, when does your visa-sponsored US job date expire?