Have you ever watched the tide coming in on a seashore?

You see a wave coming in, then it goes out again, then another comes in, then it goes out again. Each wave's starting point is a bit higher than before, and eventually the whole shore is covered in water.

That's how waves of new members are on Mastodon and the Fediverse. With each new wave, the base level of active members gets a bit higher.

The diagram below (from https://the-federation.info) shows monthly active members over the past year.