Going off what Parmandur saying, the logic is:
1. In 2000, about 20 million had ever played D&D; I believe the estimate for active players was around 5 million.
2. According to syfy.com in 2018, an estimated 8.6 million people had played D&D within the last 12 months (presumably 2017).
3. In 2020, it was estimated that there were 40 million D&D players.
4. In 2021, it was estimated that there are 50 million D&D players.
Meaning, there's been a massive spike in growth from 2017 to 2021. It may be that the 40/50 million numbers aren't only folks who had played within the last 12 months, so we can't necessarily directly correlate the 8.6M figure to that. But still, that's quite a spike.
Again, the key is that the growth has mainly occurred over the last few years, which implies a large percentage being new players.