The game obviously sold well. That's not the point. I struggle to find another example in a major franchise like Civ (I guess other than Age of Empires) where the edition from 15 years ago is getting higher play counts and nearly double the players than the shiny new version. If that's not a disaster, I don't know what is.
While I don't have an example (chatgpt claims to know many though, although I don't believe these), I honestly fail to see how this is unexpected for civ 7 and why it qualifies as "disaster" (without a useful measure provided what makes e.g., at least 3 levels of success). Was it successful, as the TT CEO claimed? I don't know, but if it was, why not provide numbers to show? I guess because it was less successful at launch than civ VI.
- It obviously needs work, as did all civ games in the past 15 years at release.
- Compared to civ VI and V, which got many years of content and patches, and have tons of great mods that enhance the game, it is also missing civs (in sheer numbers and individual) and some mechanics.
- it has a lot more competition than earlier civ games had a start. Most notably, this competition includes civ V and VI

- it advertised a core mechanic (civ switching and separate ages) that many people apparently find so appalling just by concept that (as this forums showed) are not even investing the time to find out how it actually works
- Civ 7 charged a very high price, even more than many other titles at release, and much, much more than what you pay for civ V or VI in recent years on sale.
- For some reason, civ 7 still had no sale. After 100 days, civ VI already had two, and aside from higher initial sales, these price reductions surely helped that civ VI floored a bit higher in player count (while the curve itself is similar to that of civ VII). But civ 7 is still full price, hence the pool of owners isn't growing much (while player retention seems to be similar to civ VI and V owners after 100 days, but I can only access rough data on that for the older games). Whether this is because it sold well initially or they don't want to product on sale in current state is unclear. Maybe a combination of both and other factors.
What makes me curious, on the other hand, is why the total number of civ 5-7 players on steam is lower now than some months ago. Civ V seems relatively constant, but civ VI dramatically lost a large amount of daily players, after growing for years. Some of these obviously migrated to 7. But the rest? To consoles? Waiting for civ 7 to become cheaper to change games? Tried 7 and don't play it anymore but also can't go back?