There are a lot of potential reasons it could have garnered 83 Senate votes, including vulnerable Democrats who want to be on record as being bipartisan.
Is this bill perfect? No. But just like with any other bill that has to pass a divided Congress, the question is whether it’s good enough. And to judge that, you can’t look at just this bill. People act as if this bill represents the sum total of all our legislation. If it’s not in the bill, it’s not going to happen.
We know that’s not true. There are other laws on the books which are just as much law as this one will be. There is legislation that authorizes POTUS to do much that is not contained in this bill, and likely allow him to get around much of what is objectionable in the bill.
It’s fine. Trump knows how to handle a deal, even a bad one, and get what he wants.
Also, the extension of the “debate” has given a lot of people time to ask themselves whether it’s really right for droves of unvetted people to be allowed to flood into the country and immediately go on welfare. Even in the 19th century, Irish, German and Eastern European immigrants (such as my great grandparents) who came through our ports had to be able to provide a letter from a relative or an employer stating that they had housing and a job, a modest amount of cash in their pockets (enough to get to the house), and had to pass a health check. Many got sent back.