New Delhi, Nov. 10 -- You open your investing app, type in a company name, and expect to own a small piece of it in seconds. Instead, the screen says "Watch only." No buy button. Just a promise deferred.

It's a small disappointment, but one that defines the modern investing experience.

For all the talk of "global access" and "borderless portfolios," most investors are still boxed inside the same narrow slice of the world. There are more than 50,000 listed companies across 78 stock exchanges, according to the World Federation of Exchanges. Yet the average investing platform gives access to fewer than 5,000-less than 10 percent of the global market. The rest are invisible, though their logos may still appear in your app's discovery feed....