It doesn't matter what you think of the players, when they're injured they still take up a roster spot and the accompanying cap space for that roster spot while injured.
Then you call up players to ice a full team and they also take up a roster spot and the accompanying cap space.
So you put your injured players on IR and LTIR in order to go over the roster limit and salary cap to facilitate those extra called up players. That is the process that Vegas has been using for months already.
Theodore was injured for three months and had surgery, so he was put on LTIR but was activated for the game yesterday, so Vegas needed the cap space to facilitate his 5.2 million coming off LTIR while also needing room to have roster replacements for Eichel, Carrier, Dorofeyev, Bjornfot and Hutton.
Thus, Eichel, another player who has been injured for six weeks already and also had surgery at that time, was put on LTIR to facilitate it.
That injured player, Jack Eichel, as has been said before for those who take the time to look and are genuine parties in conversation, is expected back in early March. The playoffs, for reference, do not begin until late April.