Tesla Inc. shares have doubled in three months, while General Electric Co. shares are up 44%. The pair are the two most valuable loss-making companies, part of a shockingly high proportion of listed companies that have been losing money—despite, or perhaps because of, the long bull market.

While Tesla and GE couldn’t be more different, they are exemplars of two trends driving the rising number of loss makers. Tesla shows a desire by investors to back disruptive companies as they build their sales. GE represents a growing...