It’s called subsidizing, and it’s used by governments to encourage projects that will provide a public good. While I agree that it would be ideal if the rail infrastructure was owned and operated by public organizations rather than corporations, we still get many of the benefits of the new infrastructure with much less of the costs (to the budget directly).

I would also be very surprised if the 3b didn’t come with some additional requirements that Brightline has to meet. The government is not in the business of making money, so an equity stake is way less valuable than being able to force the company to do certain things.