Just because the queue was short when you saw him, doesn't mean he's not popular at Disneyland Paris.
In fact, he's actually extremely popular at Disneyland Paris.
That's why his merchandise is the only Halloween merchandise that is being sold at the park all year round.
Two hour queues for Jack Skellington are pretty normal at the Paris park.
However I saw that you went last week, which was very quite time in general. That's every year.
So yes, that also means that the queue times are a lot lower. Logical.