Perhaps news got out that it's now possible to withdraw them more than 20 at a time if you buy a bunch LOL. I'm assuming it's part Atlantis, part Alts in general doing well, and part GPU / CPU miners essentially being shut out from mining and dumping. Though it does seem odd that ASIC miners who are, presumably, desperate to cover the cost of their purchases aren't dumping into the strength.
My theory is that the ASIC miners don't mine Dero directly. They sell their hashpower on nicehash to the highest bidder (what else would explain the large amount of Cryptonight hashpower still for sale on nicehash) and thereby earn bitcoin directly and immediately, which is what they really want, and without dumping on any market. They are therefore pretty insensitive to price spikes on individual coins like Dero. The price spike seems entirely independent, probably due to the reasons already mentioned.