If investment companies that already own tens of thousands of homes buy them and keep increasing the rent, the problem has not been solved.
You literally didn't read the article.
Build more housing.
Except they cannot increase rents when there is enough supply for a market to actually work.
Investment companies own only about 2% of the housing market, and most of these are rented out. Investment companies aren't really the cause of housing prices remaining high - in moderate- and high-demand areas, we simply aren't building enough to keep up with demand.