The only reason I would even remotely consider it is if I already had gigantic investment in Jira, and even then I'd strongly consider doing something else and writing up a small sync tool to keep task statuses updated.
Anything that requires time or money for less than 10 people.
Notion has similar problems (search sucks, performance doesn't scale), but starts costing once there's more than one person. You go from £0 to £20/mo for two people, and the chances are that at two people you're on ramen money so you don't want to be spending on... anything. Mediawiki and co require a VPS and auth/vpn/management. That's a distraction you don't need for the first 6-12 months of working at a startup. If I as a startup CTO/founding engineer spend 2 hours setting up mediawiki to spend £60 in a year on, the payback vs confluence or github wiki (which is running in seconds and is free) is when you scale to 10 people. Move to something when you have an actual need for it. By the time you're spending $64/mo on confluence users (or £100/mo on notion - sorry for currency switch but confluences pricing is only in USD for me), you're spending 10x that on payroll _management_. It's just a nothingburger.
There are companies that offer mediawiki as a SASS app. You can self-host if you want but you by no means have to.
I'd agree that most startups probably dont want to bother with doing their own setup as they have more important things to focus on.
[Disclaimer, im a mediawiki dev]
I’m not saying it’s 100% of startups, but unless you have a good reason not to, I think confluence is the right choice.