No processing done at the DB very often implies more queries and consequently a higher workload in the DB than just doing the processing there. That's evident when looking at typical ORM usage (usually very chatty applications).
Also very often doing the work in the DB means a simpler solution, fewer race-condition issues, and less work overall.
When talking about this particular case, the CHECK constraint, it is probably matter of measuring the impact and understanding at which point this might be relevant, and considering the cost of the alternative implementation at the application layer
Toon Koppelaars shows that in a few experiments done with Oracle ( https://www.youtube.com/watch?v=8jiJDflpw4Y&ab_channel=Oracl... )
Also very often doing the work in the DB means a simpler solution, fewer race-condition issues, and less work overall.
When talking about this particular case, the CHECK constraint, it is probably matter of measuring the impact and understanding at which point this might be relevant, and considering the cost of the alternative implementation at the application layer