Why take the chance of moving up and ruining what he currently has? It's not like he's cleaned out his division, and he hasn't been champion for long. Let him get in 2-3 more wins then worry about moving up. Look at his opponent, Manny, who didn't do too well in LW but when he moved to the WEC he was wrecking people up until Aldo. Not everyone can be Anderson Silva, just because your dominating in your own weight doesn't always mean you can move up and do the same.
With that being said, I do think Aldo would wreck Florian.
Don't be surprised to see Florian calling out Aldo accusing him of being scared. I honestly think Aldo turning away the chance was a blessing in disquise for Florian. If Aldo would have fought him, Florian wouldn't be able to stand for three weeks.