It's not just Monero, but popular privacy coins like Zcash*, Dash, SCRT, etc are also pumping.
Zcash already dumped, but it all began with Zcash.
So the question is, why do privacy coins pump? Well, perhaps because of countries pushing KYC/AML aggressively, and people don't want to stay visible, or perhaps it's just market seasonality.
Monero is what could be called a privacy currency. Zcash* and Dash also promote themselves as privacy currencies, but transactions using them are easy to trace.
If the question is why Monero is gaining up, it's several months behind. Bitcoin broke its all-time high months ago.
Why now? It might be due to Full-Chain Membership Proofs (FCMP++).