Stupid that you have to go through MS store for extensions for Edge.
Any reason why you object? Browser extensions are an obvious route to introduce malware, so all the major browsers have moved to a trusted extension ecosystem for non-developer/development editions of the browser.
Chrome extensions must now be installed via the Chrome web store. Chrome has already discontinued support for binary extensions other than the Flash plug-in bundled with the browser, which is already due to be be removed in the future.
Firefox add-ons for the release version of the browser must be digitally signed by Mozilla; I'm not sure if the about:config work-round to allow the use of unsigned extensions still works in Firefox 48 as I no longer have any need for my old unsigned extensions. Mozilla are in the process of deprecating the external binary extensions API; the only non-bundled binary extension that works in the relatively new Windows x64 version of Firefox is Flash (so you cannot use Java with the x64 build of Firefox), this restriction is due to be extended to the x86 version in a future version of Firefox, and Flash support will eventually be discontinued entirely.
As the move to trusted browser ecosystems with no external binary extension support (beyond Flash for a limited period) has or is taking place in other browsers, also Microsoft had the advantage of a clean start when implementing Edge extensions, it seems obvious for Microsoft to use a trust system based on the Microsoft Store infrastructure for Edge extensions. The barriers to getting a Microsoft Store account to distribute an extension are fairly low.
I would rather we lived in a world where trusted computing was still unnecessary, but I think the case for technologies like UEFI Secure Boot and closed browser ecosystems is now compelling considering what we know about the threat environment. Unless security is either mandated or the default, most users will stick with insecure default options out of ignorance, lethargy and/or performance concerns.