It is like how someone was asked to write a poem that would hold true for all time and be relevant everywhere. If you write a poem only for a particular event or festival, such as Diwali or Holi, then you can sing that poem only during that time. You cannot sing the songs for Holi during any other festival, isn’t it? Such songs are for special times and specific occasions.
But some songs are such that they can be sung at any time. So our scriptures were written keeping in mind that they should be relevant everywhere and at all times.