It wasn't stuck at just the icons, it let you expand to see words as well. It was much better in my opinion and I rarely had it at the collapsed state like his screenshot shows.
Click-to-reveal and hover-to-reveal require manual dexterity, a curiosity to see what's behind a link, and time to discover and parse the new visual information. Making these cognitive demands, particularly on sites where users relax, is going to reduce engagement.