Monopolies are rents, in the sense that a network effect isn't something that the company built, but is surplus value it's gained access to and can extract. The situation is exceedingly path dependent and often rewards little other than luck or ruthlessness, with monopolists retaining value not by continuing to innovate, but by choking off, buying, or outright killing competitors.

Why do the consumers deserve government subsidy to protect them against negative effects of monopolies, but not employees or small business owners?

Well for one, the government isnt subsidizing anything. They are instead allowing customers to do what they want with their money.

And 2, I don't care what happens to business owners. They are wealthy enough to handle themselves. (Yes, if you are even a small business owner, that still counts as "wealthy" in my book. Most people don't own much of anything)

And 3, we are talking about a product monopoly, and not an employment monopoly. Nobody has shown any evidence that Amazon has any sort of monopoly on hiring people. People are instead arguing that they have a monopoly on the markets that they sell in.

Consumers deserve the protections because they are much less well off than either large or small companies.

You don't need the government for that - you just let people do whatever they want. Any sort of anti-monopoly legislation is a subsidy in a sense, because it gives those protected some degree of economic power that they wouldn't otherwise have, enabling them to make better deals etc. And there's nothing wrong with that in principle, if you believe in common good - but then the question of scope arises.

And we're talking about all kinds of monopolies. The effect that Amazon has is not so much on its own employees (although there are some obvious issues there as well), but on employees of all the competitors that it puts out of business. All those people also benefit from the lower prices that Amazon offers - but that is more than offset by the loss of income. It's kinda like Walmart - it's more affordable, but at the cost of making a lot of people poorer such that they need that high affordability. For the owners, it's a win-win, of course, because it creates a lock-in. But I don't see why we should accept that as a society.