You misapprehend self interest, confusing profiteering with investment. Investing for capital gains depends on self interest, but not only for investors. The operators of business seek investment to improve the conduct of their business, and their self interest dovetails with that of investors intent on capital gains, who inject capital into the business by purchasing the underlying investment vehicle, such as stock or bonds, and seek to enable the business conducted to compensate them for their investment by increasing the value of the stock, or paying the interest on the bonds.

Steem does not facilitate this mutual cooperative benefit, simply extracting the value of the content created and using substantial holdings of the underlying investment vehicle to manipulate rewards as allowed by specific code. That code is not human nature. It is a mechanism that can be different, and potentiate self interest to be cooperative and mutally beneficial, rather than parasitic and extractive.

The devs were not experienced investors, and simply chose the easiest route to ROI, despite that being contrary to capital gains, which are far more productive of ROI over time.