I agree that it doesn't need to be about security. If web apps had to be installed on browsers similar to the way they are installed on the operating system, they would be acceptable. The current system that they run automatically when you visit a web page is obviously unacceptable, but that could be changed. The lack of standards and GUI features is also not that bad.

For me it's more about pricing and freedom. Server and computing costs force most web apps to be subscription-based and I'm extremely picky about subscriptions. First, there is often data lock in, of course, and it's often very deliberate with no viable export options. That's unacceptable to any reasonable person both on desktops and with web-based apps. Second, subscription-based applications are universally too expensive. If I turned all desktop software I currently use into equivalent subscriptions my monthly bill would be insanely high, an additional 200 to 500 euro per month. To most people including me that's just not affordable. It just doesn't add up. There is no market where people buy 20 different apps at $15/month each.

Almost everyone uses free desktop apps and a few paid ones.