Apps won't stay where I left them if I change to a different app.

Let's say I'm using TikTok and pause a video to check a different app. I'm done with the second app and return to TikTok expecting to find the paused video waiting for me: no such luck. I get the launch screen, and the whole thing reloads as if I had opened the app again from scratch.

I've seen this happen with a few apps. When it's my bank's app, I think it's for security, which is fine. I don't know why it happens to normal entertainment apps.