Being loud vs being heard

MENTION Greta Thunberg, and her outburst at the United Nations springs to mind. Since the footage of her lambasting world leaders went viral, she has gone on to be named Time's Person of the Year, and was nominated for a Nobel Prize.

Bring up Boyan Slat in a conversation, however, and you'll probably get quizzical looks, and a "who's that"? CEO of The Ocean Cleanup, Slat invented the world's first ocean cleanup system, but remains relatively unknown.

For all the work that Slat has done, why has he not received the attention that Thunberg has?