Coming from someone who is a hardware/firmware engineer, that's also what I'd do.

Developing hardware is hard and costly. If you are looking to create a consumer-based product, this would be especially true. There's no way you'd be able to manufacture your product as cheap as getting a manufacturer to supply you with a OEM version of their product, let alone having to amortise the R&D cost spent in developing it! And generally speaking, the cost is the bottom line in a consumer-based product.

This is what the Wyze Cam does. They've created a really nice product, but there's no way they'd be able to sell it for $25 had they also developed and manufactured the hardware themselves.

I’ve heard that a significant proportion of kickstarter projects do exactly this

I've searched numerous times, but could not find anyone doing the thing I want to build. That's why I'm playing with the idea of doing it myself