It depends on a lot of factors though. Creating your own engine is by far not an easy task. The more feature rich it shall become, the more work it will need. Especially if it should have high 3D graphics quality while also running performant. That alone can cost a good team at least 2 to 5 years.

Switching engines also depends on how portable your work from the old engine is with regard to the new engine. It may not be impossible but can still be a lot of work. The earlier that decision is made, the better.

If the devs are determined enough they can surely do a switch. But they might sweat a lot. And especially for smaller studios, or studios without sufficient funding, this quickly becomes a matter of financial survival.

So it's not impossible, yes. But don't take that lightly as well.