I think the main reason is distribution. Desktop apps were/are difficult to distribute. To get an desktop app into organisation, you either needed to tell people to install something, and they need disk space, RAM, different versions of Windows, might not work on Mac, almost never on Linux. Then they need to update the app regularly somehow, still not solved for all apps. Bigger orgs have managed distribution, but then smaller groups can’t install things without going through IT. Then you’ve got servers, which require someone to setup, maintain and have their own lead time. Webapps, especially free ones, have none of these issues an individual can just start using it. Webapps mean everyone using the latest version straight away.
Phone apps seem to be modelled on webapps, typically the server is run by the app maker, installs are easy and updates are automatic. Additionally, phone apps automatically go on the home screen and have notifications, which means you’ll open them more often.
Additionally, in the 2000s we had IE-only webapps, meaning that when companies only cared about Windows clients, they still thought making webapp was a better way to reach their customers than a Win32 app.
Phone apps seem to be modelled on webapps, typically the server is run by the app maker, installs are easy and updates are automatic. Additionally, phone apps automatically go on the home screen and have notifications, which means you’ll open them more often.