Philosophy, Architecture and alternatives.
The philosophy of the program is based on users having full control of their files which are kept locally on their own computers. Obsidian neither stores nor transmits any of this information.
As I understand it, the program is developed in electron as a local app rather an extension of a web app. It seems likely that considerable work would be required to create a web app, and where would the web app go to access files? If, as was originally suggested, it was in Dropbox or G Drive, who would control access to those files? Presumably the idea was that the app was given the access details and could sign in itself? There would be a major speed issue because the files would be on one web server, the program on another and the suggested users would be somewhere else working behind a corporate firewall. Probably the program would have to limit the number of files it loaded to make it usable. So it looks to me likely that it would be a lot of work for something that would have performance issues. There will be mobile versions of Obsidian, but Silver has emphasised that these would be lite versions of the app; partly I assume because of the limitations of phones and tablets, but presumably also because of these other issues.
Most other programs offering a similar feature set are web apps and run on a database (and despite this being a fundamentally faster design than the one just described, Roam has been accused being slow at times). But this availability does mean that people who need a web app have other options available.