But have you ever stopped to think about it from the publisher's viewpoint? Even if your book is any good – and it's unlikely to be more than "promising" to start with – it might not be the sort of thing that the publisher's reader enjoys. Either way, reading your manuscript is most definitely "WORK". Workers rightly expect to get paid.
Now think about how long it takes you to read a novel. Let's make it easy, take a short one like F. Scott Fitzgerald's The Great Gatsby. That's less than 50,000 words long. Sit down and read it in a day, perhaps? That sounds like 8-10 hours to me. The minimum wage in the UK (from April 2019) is £8.21 so that's just £65.68-£82.10 payment. Bear in mind that's a masterpiece. Yours will take longer. And people who read manuscripts are usually pretty highly-qualified and expect rather more than the minimum wage. Plus they have to make up some sort of report and send a reply to the author. Plus they're entitled to holiday pay and so on.
That's why agents and publishers have to be brutal with submissions. Simply to survive, they have to cast aside anything that doesn't grab their attention immediately. And expecting them to do it for nothing, or for next to nothing, is really a bit insulting. You wouldn't.