Why do we need a browser OS?

Now there are a large number of browser operating systems , many - it opensource projects. The most interesting thing is that where they are not mentioned about them - only bad reviews are everywhere, like nafig is needed, and why they were invented. But really - why?

Operating system, OS (English operating system) - the basic complex of computer programs that provides control of computer hardware, work with files, data input and output, and the execution of application programs and utilities. ( Wikipedia )

Modern browser operating systems have pretty good functionality. Watching videos, listening to music, simple image editors, fairly advanced text and table editors, games, FTP and mail clients, messengers, various useful utilities, etc. And for example, one of the rather developed browser operating systems is demo.eyeos.org

Is this not an option for super cheap laptops? The lack of a hard drive, a weak video card, a minimum of RAM - and here you have a computer for a few tens of dollars. All he needs is a permanent Internet connection.

The second application is virtualization. On one machine, even without a hard drive, you can run several such OS.
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It is possible to write an “OS” consisting of one browser, which will immediately join the remote server and “load” the OS itself.

Yes, now there will be opponents of this idea who will be against the whole idea in general. Security and all that ... But not every one of us stores such important data on a computer as to worry about security.

And now what the topic was created for. What application of browser OS you see?