Historically, indica strains come from parts of the world where the growing season is foreshortened by the harshness of the elements. Those plants would need a pretty accelerated life force to grow, flower, and produce viable seed to ensure the survival of the genetics.
Sativa is more of a temperate/tropical species, growing where the environment is more conducive to a longer lifespan, closer to the equator, latitudinally speaking, more sunlight, longer days, shorter nights, different growth cycle altogether.
I've been planting the same strain of indica outside for twenty years now, never crossbreeding it with anything, and it's still as good as ever.
Ever grab a plant by the cola, jam your face into it, inhale, and feel like you've just been spotwelded to the ground?
'Old world' vs 'New world'-give me the old!