This is an issue I see at a lot of companies make, even going further than self-hosting. For example replacing off the shelf software with an internal product.

This is an issue I see at a lot of companies make, even going further than self-hosting. For example replacing off the shelf software with an internal product. "This is not good, we have to do this ourselves". And in the end it costs way more, and you end up with an inferiour solution because it's not your core business, and nobody really has any time to work on it. Very sad really. The first thing to ask is exactly what you asked here. I can't upvote this enough.