People underestimate the cost of switching game engines.

While a lot of concepts are transferrable between engines, if you've got a team of experienced C#/Unity developers who haven't touched UE, switching to C++/UE is likely to cost a lot of time/money. A new engine can still be a steep learning curve for experienced game developers. You might be able to pick up the basics over a weekend, but reaching expert levels of knowledge takes years.

That cost increases further if it means restarting a project from scratch rather than building on top of an existing codebase (which will likely include not just the game itself, but also an assortment of tools built within Unity for building content and improving workflows).

Unity's killer feature for many is still its C# support. If you're a small team or solo developer who doesn't need AAA levels of performance, it can be a big time-saver over working with C++.

That's one of the reasons why Godot started brushing up their C# support recently.

For that that small/solo team it's also easier to switch engine and since they can't get custom license deals like the big boys having the same language may encourage some to invest the time and resources.

I presume because they already used Unity in Cities Skylines (the original), and it would be easier to build and improve on the previous edition instead of throwing most of it away and starting a new project with a new engine.

Wouldn't say its known for performance issues but it certainly is known for scale issues in open world games (Things like moving too far from 0,0,0 causes polygons to flail and physics to break, so you need to do tricks to work around that) which feel like the sort of thing you're going to encounter on a game world that exists from person scale up to plane scale.

In Outer Wilds, the player stays at 0,0,0 while everything else moves around them.

https://www.youtube.com/watch?v=LbY0mBXKKT0&t=1907s

I was under the impression this is how things always work in graphics pipelines. You don't want to give up on all the precision between 0 and 1

They were already entrenched with their first game, and used that opportunity to buy into the DOTS hype.

DOTS had a much troubled development cycle; most of what was promised was eventually abandoned, and the key people were laid off. Anyone that bought into it is now stuck in the hybrid-DOTS limbo, where they have to invest substantial amount of time into making the engine features work.