You're half right.
The goal is to crush their opponents in an election, so they have the time and space to enact their policies, and get the credit for them. The NDP have been propping up an ineffective and unpopular LPC, while the LPC claim all the credit for the legislation that does become somewhat successful. If the NDP was getting credit for their efforts it would be reflected in the polls... It isn't, which means their strategy is not working, and realistically was never likely to be successful.