That, and the player base stuck around. 14 years old, and put out to pasture ("maintenance mode), yet daily logjn count is still a respectable ~250k or more.

The real answer may actually be something like the Whales are still addicted and buying lots of in-game silver. One viewer donated over $5k USD to Aztecross's stream during the announcement recap, then someone else threw in $500+. D2 has enough sleazy gacha mechanics going on that a lean dev team might be funded nicely by whales.

[edit, popularity.report daily logins around 250k in the last 24h, 40k in the last hour, and fluctuating from 20k to 75k per hour]