Commission for NoSleepNeeded
Sometimes, succubats need to make a new queen; whether because a hive was destroyed, or because a living queen wanted to establish allied hives. When these times come, the new hive needs a new queen parasite.
A queen parasite isn't born, it's raised and nurtured. A crown crab given specific care and time to grow and develop can become a queen. Every parasite, and by extension, every experienced host, knows how to do it. The reasons new queens aren't constantly popping up are 1 - Loyalty, 2 - Succubats know how difficult it is to feed a queen., and 3 - If your old queen is still alive, it's a lot harder to rebuild using old hive-mates.
It's fairly common for succubats to become the new queen. They know how to make the parasite, they already have hivemates feeling the pull to help a queen, and it's better than gambling on a new host who doesn't know what they're in for.