Warner Bros. didn't say why it yanked the two titles, although Lego: The Hobbit has a less-than-stellar history. It only covered the first two movies in Peter Jackson's trilogy, and plans for an add-on that introduced The Battle of the Five Armies never materialized. Kotaku observed that both Lego games were free at the Humble Store in December, suggesting that Warner Bros. might have been phasing them out due to low demand. They're not the most recent games (Lego: LOTR arrived in 2012), but other Lego games have held long shelf lives -- clearly, some franchises have fared better than others.
Update 1/6 11AM ET: Polygon speculates that the licenses for the games expired, although that's not confirmed yet.