From the article:

> … but also in browsers because some living room devices today have just an HTML5 browser and don't even have flash space big enough to put our native C++ engine.

Ask the people buying and making those devices, not the people trying to get their services to work on them.

The answer is probably "because the alternative is worse". I too would rather make a single web app than separate Tizen/tvOS/WebOS/Android/whatever Roku runs apps.