Why did slaanesh's birth not attract the Tyranids?

So if I understand correct, the big psychic pulse from the Pharos beacon is what rang the dinner bell for the Tyranids to make a quick detour to the galaxy. If that wannabe astronomicon was enough to draw their eye, why was the birth of a chaos god, which broke reality permanently and happened at basically the same time, not what drew them in? I'm all for space marines fucking thing's up for everyone but it seems like slaanesh should've been the big draw. In terms of intergalactic travel 5k years is nothing, so she should've been a lighthouse for anyone and everyone even slightly attuned to the warp, right?