When service deleted the parameters of this service not deleted (in database)

when we create a service with parameter, and after we delete this service.
The parameter is not deleted, They are always visible in database. (propertyentry, propertystring)

SQL :

select * from propertyentry where entity_name = 'ServiceConfig'
select * from propertyentry pe, propertystring ps where pe.id = ps.id and pe.entity_name = 'ServiceConfig'