Great product managers are very valuable. Having someone who knows the customers and the market inside and out helps a company focus their roadmap on the highest value features and products. If you're paying 50 engineers and their managers to work on products, having one highly-paid person dedicated to scrutinizing every last detail of the roadmap to make sure you're not wasting time on the wrong features will produce an efficiency gain.
I think the issue is that there are a lot of bad product managers out there, so chances are good that most people have never actually worked with a good product manager. Product management is a vague position where quality is hard to measure, so a lot of people end up in Product Management because they know how to speak charismatically and present themselves well in meetings.
Anecdotally, the recent downturn has forced a lot of companies to take a closer look at these highly-paid soft positions. Among my personal network the number of engineers who got laid off is much smaller than the number of product managers who got laid off, despite the fact that I know far more engineers than product managers.