It’s a visa they give to foreigners who they think have training in science, technology, engineering, or math (STEM). IT is ‘information technology”, one aspect of the STEM category. They come to our country and take American jobs even though we have huge numbers of workers trained in those areas.
They are desired because they take half the pay that the market is paying. First, their ‘degrees’ are suspect. Second, their “English” certifications are a joke.
Not only that but employers require American workers to train their replacements or give up any severance package they've been offered. It made big news when Disney did this but it's been going on for several years. It's a complete abuse of the system. These visas are only supposed to be issued to fill gaps where no qualified American can be hired to fill the job.