There's a fundamental priority difference between webOS and iOS/Android.
Let's first take a look at macOS (this basically applies to Windows as well). How do you open an app? First, you check the dock for commonly-used applications. If they aren't there, you search the applications folder (or launchpad in newer versions) or use +Space to search for it. Notice that dock offers direct access, but other apps require extra steps.
Window managing is what a desktop OS is all about -- NOT opening apps. You have Spaces/Mission Control to group apps (because positional memorization is important to humans -- I suspect 2D spaces were superior in that regard to the 1D mission control desktops). You can drag windows around, resize them, put them side-by-side, etc. Closing Apps is also first-class with with just a +Q. Notifications are unobtrusive popups. Minor settings are available in the tray and major settings in Preferences (accessible by icon).
webOS follows that paradigm closely. Common apps go in the launcher. Less common apps are either in the app drawer or JustType to search for it. Launcher offers direct access, but everything else takes extra steps.
The primary view for webOS is for window managing. You have a 1D set of apps that you can move into Groups. Closing apps is a simple swipe up. There exists room to add things like side-by-side apps, but most of the devices were never big enough. Notifications are unobtrusive popups. Minor settings are available by clicking on the tray. Major settings are available in the settings view and accessible by icon.
The reason the webOS UI is so good is because webOS is the desktop paradigm you've been using for years.
Android and iOS have adopted many of these patterns, but they still feel foreign. Why? because launching apps reigns supreme. Instead of multi-tasking being the default view, their default is showing apps on the home screen. To change tasks, you have to switch into another, secondary mode and then back out of it. Android's and iOS's UI paradigm is upside down. First-class app opening with second-class task managing is bad UI.
In webOS, users tend to close uncommon apps and leave their common ones running which makes freeing resources the default (good for constrained systems). In iOS or Android, users simply cannot be bothered to use an out-of-the-way, second-class task switcher and don't even realize there are dozens of open apps.
Instead iOS/Android app icons become a poor, ad-hoc task manager that is ill-equipped to manage apps and completely unable to kill them.