A lot of figures like this are not accessible publicly either for privacy reasons and/or because how requests are being routed.
The operator of a feed can record & track requests from DIDs and count the number of daily/weekly active users as number of DIDs.
RE: 
Bluesky Social
Rob Ricci (@ricci.io)
- I'm not doing that
- see: https://discuss.systems/@ricci/115171236116610436
- yeah and people seem pretty set against trying to get them for some...