Because she's SUPER PURTY.
Especially that new skin.
http://am.leagueoflegends.com/image?f=http://ddragon.leagueoflegends.com/cdn/img/champion/splash/Elise_3.jpg
Also while it's purely speculation, I suspect that in 5.1 or 5.2 we might see some tweaks to the difficulty of the new jungle so that other junglers are more relevant. If Elise's jungling gets any easier, she'll be prime real estate for the next #1 Jungle pick, because right now she's just shy of being awesome. If it gets to that point, you can use her spiderlings to tank, then go full assassin mode instead of building tanky, and then your team won't have to run an assassin in every lane, like they do now. In the current meta, the Jungler has to be innately tanky because otherwise you just aren't jungling. If Elise gets to be an assassin again, it could get very interesting.