Remember when everyone was clowning on the trailer for this movie because they said "Throughout the years we have never interfered, until now." and people were saying things like "the Thanos snap wasn't enough to interfere?"... I think after seeing Loki, we have a good idea of WHY it is that they interfere only just now and that's because, honestly, Thanos wasn't enough of a threat for it to be worth their time. Sure, half the population got eliminated, but society was going to live on. What we're dealing with now is much larger than that.