Virgin trees: Most seeds never sprout unless conditions are perfect, take forever to grow, a few bugs can kill an entire tree, need complex biochemical pathways to survive winter.

Chad grasses: Can sprout literally anywhere, grows whether you want it to or not, literally grows faster than things can eat it, outcompetes tree seedlings, brute force method to species survival, can afford to just die in the winter knowing more of them will crop up next season.