Why would they not bother trying to win a trophy when they'd fought so hard to get to the Final? It's not as if they win trophies every year and can be complacent about it.
The plain and simple truth is that they can't play at 8/9 out of 10 every week because they're Livingston. And the same applies to St. Mirren, Kilmarnock and all the rest. They can't operate at a high level every week. If they did, they would be playing at a higher level. They're not at their level because of a deliberate attempt to be inconsistent simply to infuriate opposition supporters. They're at that level because teams at that level are, by definition, inconsistent. If they were capable of delivering a high level of consistency, they would be a better team.