Youre dealing damage, using your mana as you see fit, and guess what
If your opponent has a card like Ashnods Altar or High Market on the board, they can just sacrifice the bug to get their commander back into the Command Zone, making your play a waste of mana
For Blessing of Frost to work its magic, you want to be playing cheap creatures with power and sizeable three-drops, trying to close the game quickly, and only playing basic lands or Faceless Haven
Cost reducers like Herald's Horn, Urza's Incubator, and Patchwork Banner not only make it easier to cast your spiders, but they also make sure theyre stronger once they land
As the time streams grew more and more unstable, Dominarias creatures struggled to adapt