Being good at SQL, data visualisation and extracting insights is like being good at navigating with a map. The thing is, someone needs to make the map in the first place - a system of metrics - and that's a totally different skill. It's something you rarely get exposed to because in established companies, a system is usually already in place. It also doesn't help that there's lots of content on defining some north star, but not so much on defining a group of metrics to capture your business as a whole.
I'd wager that most folks start naively. You care about user or revenue growth, and perhaps knowing if you are default alive or dead. That's a good start, but these are output metrics. They aren't actionable on their own and you need more granularity to investigate why growth is the way it is.
So you start looking at things that are interesting or feel obviously important - daily active, daily uninstalls, monthly active, retention curves, power user curves and so on. Not too far in, things get messy.