1. For people like you that don't want to install them, they're just a normal website.
2. For people that do want to install them for the added functionality (things like notifications), then it is easy to install, and furthermore cheaper for developers to build and maintain (one codebase instead of multiple).
You say "you have no desire to have an app", but I think for most people that's really dependent on the site/application. Yeah, for any site I just have a short term or infrequent transaction, I don't want an app either. But many/most people use apps for businesses they have long term relationships with (namely financial institutions).
In short: most devs' simulacra suck.
Check out:
https://developer.mozilla.org/en-US/docs/Web/API/Navigator/s...