Merging both views is essential here: the length of a stay and the choice of season are not isolated variables that simply the budget dictates.
We must combine the idea of budget constraints with experience expectations to truly understand travel decisions.
A shorter stay in high season in Brussels can cost more per day than a longer stay in low season, but the cultural experience might be richer.
One does not go without the other; they cannot be artificially separated as if there was only one determinant variable.
For example, for a school trip, I have to juggle between the cost of the accommodation and the availability of educational activities, even if the low season is tempting for costs.