It costs more time to fix bugs after deployment, when the errors were not caught during testing. It costs more time fixing requirements during development, when they were not properly analyzed by customers and consultants. It costs time that is lost on team (re)planning and task-switching when projects have not been properly announced to a resource manager.
Our employees should not accept work that others before them have not properly prepared. It reduces efficiency and productivity in the pipeline, and it demotivates people because they will then fail to spend the time they need themselves for completing their own work. It results in an ever-growing avalanche of work that was not completed properly before being sent down the pipeline to the next victim.