Tor Metrics: number of unique onion addresses v2 vs. v3

Hello all,
I was just wondering how many hidden services there are. On Tor Metrics it shows that there were about 130K v2 onion services before v2 is no longer available in the new Tor versions. As of November 2021, Tor Metrics also shows v3 onion services. All at once, there are more than 600K v3 onion services. Currently there are over 770K. How to explain the big difference?