They dont have many cards that matter
On a naked board, you can toss a +1/+1 counter on something
Massacre Girl, Known Killer and Syr Konrad, the Grim can abuse all this death to draw cards and obliterate life totals
The one big, expensive addition to the non-budget build is Cavern of Souls, and while the card is great against control and pretty close to a free roll, since Lead the Stampede is the only non-Elf card in our deck, it's probably not 100% necessary
This four-mana sorcery gives all your creatures not only infect, but also +1/+1 and trample until the end of the turn
At most levels of casual play, getting back two creatures for three mana is a hell of a deal, especially given so pairs of creatures can either synergize or straight up combo