There are two primary scenarios where shitcoin garbage alts pump.

1) Market has been down only and the shorts that have ridden them that entire way down finally get squeezed. This usually happens at the start of runs

2) Market has been up only and longs that have been riding it up the entire way have nowhere left to rotate to except garbage that hasn't pumped yet. This usually happens at the end of runs.

It seems clear to me which one we're currently experiencing.