Because against Liverpool we were happy to defend deep and played for a draw taking what could come along.
Today we tried to win so it's possible to change tactics/team.
It's possible to change tactics/teams but you didn't explain why we could not use a similar tactic/team against West Ham. In fact I have an other question, would it be inconceivable to use the more stable and coherent organization that we used against Liverpool and build from it instead of going back to an approach that has been really bad all season?
I should add that if we played for a draw more often, we would have far less losses this season, 8 losses in 18 league games is a pretty high record.