"In many cultures." This is agreement.

Holidays, for Trowa, are mostly things that have meaning to other people. He sits back and observes this habit. This used to be even more true than it is now.

It's also one reason why Catherine gets to bustle about and steer everyone towards the tree and PRESENTS!!!, and Trowa will play laconic cultural interpreter if needed.

(He's letting himself be steered, though.)