Did one of your spellcasters know the Gate spell? If so, what stopped the PCs from pulling the BBEG out of their lair and beating them up from the comfort of their homes?
Anti-magic field?
The BBEG has taken great efforts to hide their true name?
Private Sanctum spell?
The fact that Gate is an inter-planar spell, and not an intra-planar spell?
As the GM, one of your jobs is to present challenges for the party to overcome. That means actively countering their abilities list just as often as it means giving them a bone and letting them shine. The big moments of flexing mean a hell of a lot less when all they do is flex.