Guard probability for exit nodes is > 0 since July/August 2024 consistently - Why?

Current Tor lore has it that exit capacity is scarce and therefore exit relays with the Guard flag have a 0% chance of being picked as Guard nodes. While this has been generally true (with small exceptions) it seems that assumption does not hold anymore since July/August 2024. See: e.g. the probabilities/fractions for dotsrcExit7:

The question is: what's going on here? (daily business in the network-health world :))