Yeah, it depends of the malicious activity daily, sometimes You get new signatures almost every hour or every 2 hours (default schedule), and days as yesterday that thrre is no new signatures for hours... or maybe They were just running maintenance...
As far as I know, signatures depends a lot on human resources to analyze each UDS detection and verify if it is correct to update to database.
This depends on human (coronavirus) and malware activity.
As you said above, Kaspersky product always check for updates and the version of databases only changes if got big changes. I think they only add to the same database if there is no new malware or something.
You can check that software always download something every 2 hour, KB or MB, but databases doesn't change.
And I noticed the same thing as you: there is days with a lot of databases changes, and days with 2/3 new versions.