It wasn't sudden, it was a slow roll since september,   I noticed it when i stopped mining monero back in october when the unknown mined blocks was only like 40% back then,  but it made monero far less profitable so i switched back to duel mining eth.  For the past 3 months Baikal has held it
at 75% of all the new blocks,  I guess they thought no one would notice.   They are only selling them now cause of the monero fork
coming in 2 weeks,  hopefully  the fork will make these miners worthless space heaters.