Glad you pointed that out. And, in the most prevalent application of Conway's law[0], those changes enabled and are entrenched by the "agile" practices in software development. Incremental work, continuous deployment, endless bugfixing and webapps fit each other like a glove (the latex kind that's used for deep examination of users' behavior).
It also enables data siloes and prevents any app from becoming a commodity - making software one of the strongest supplier-driven markets out there, which is why the frequent dismissal of legitimate complaints, "vote with your feet/wallet", does not work.
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- Very high latency
- No support for online updates
- Impossible to easily administer
Cross platform was much less of a big deal when web apps started to get big. Windows just dominated in that time. Not many people cared about macOS Classic back then and desktop UNIX didn't matter at all. Browsers were nonetheless way easier to deal with than Windows itself.
Agree that killing piracy was a really big part of it. Of course, you can implement core logic and shared databases with non-web apps too, and the web has a semi-equivalent problem in the form of ad blockers.
All of these (except logging on to the same data from all my devices, which is nice) benefit the developer at the expense of the user.