This particular case could be a couple tables in a database. To follow proper encapsulation guidelines, it would have to be front-ended by some stored procedu

This particular case could be a couple tables in a database. To follow proper encapsulation guidelines, it would have to be front-ended by some stored procedures, so that the underlying representation is free to change. How would you roll out this change to production? If you just swapped out tables and stored procedures, you'd have downtime. You can't just install a parallel table and stored procedures, because there is no way to tell all of the consumers to use the v2 of your functions. So you'd have to temporarily remove availability of the WorkingDays functionality. If it were deployed as a microservice, you are free to deploy a v2 of WorkingDays in parallel. When it's live, the old one goes away, and there is no loss of availability.