People forget that there wasn't even a mass exodus from Digg. Although we can pinpoint the exact day that Digg killed itself, it actually took a long time for everyone to eventually leave. People hedged their bets between platforms -- just as many people are doing now between Reddit and all the new alternatives.
This week on Lemmy actually feels very different from last week. There's some sort of critical mass that has been hit even if it's just some minuscule tiny fraction of the total traffic of Reddit.