That's the beauty of working in a tech company compared to a non-tech company. Every single manager in my org is a former engineer. Every single manager above them is a former engineer. Heavy majority of directors in the org are former engineers.
In the world of early and middle stage startups, you're probably right. However, in massive tech companies or more legacy-type tech companies, it seems like you're a lot more likely to find managers who are trained as managers and not engineers (MBAs, etc.)