To be fair, whether or not you understand SQL, it does integrate spectacularly poorly with most programming languages. Sure you can use ORM, but a massive cost of capability and performance.
Database rows simply aren't objects. You have to squint so hard you risk retinal detachment before the two are even a little bit the same.
Other database paradigms exist, and have existed for a long time. File systems spring to mind. The Windows registry is another.
A case can at least be constructed for using something other than a relational database if all you want is to persist objects in a consistent manner.
I guess since NoSQL isn't new anymore, maybe the database choice at startups is sensible again - as they try something new in another area?