If I buy a phone from you, and then download an app that bricks it, I want my money back from you.

Yes, you can argue that I'm responsible for that, but consumer protection laws will apply, and there's going to be a court case, possibly even a class action suit. Too many uneducated users who refuse to take personal responsibility for their actions. Yes, it's not ideal, but this is how people are.

Your response has at some point got to include vetting the software that your users can download onto their phone, for purely financial reasons.

If I buy a laptop, and then install Linux on it, and download a malicious package and install it, then that's on me. If someone buys a Dell laptop and downloads a malicious application and installs it, then Dell support gets to deal with that problem. After a while, Dell is going to install some software by default to help with this, and spy on what users have been doing purely so that if they mess up then Dell can help. Eventually this happens enough and Windows gets an app store, and fairly soon after a version of Windows that can only install apps via the app store.

This is not about control for control's sake, or revenue (except saving support costs). This is about protecting people from themselves.

But sure, if Pine can put a big sticker on the phone saying "do not install anything on this phone" and make that legally binding, then they won't need an app store.