Why is the walltime is set by default?

I was wondering why the default walltime for workers is set to 30 minutes instead of None?

For example, see https://github.com/dask/dask-jobqueue/blob/1f9ae1ecc79a5b76930e56c8801f3b8ace659877/dask_jobqueue/jobqueue.yaml#L71

I kept having failed jobs for 2 days until I realized that it's actually this library is setting a hard limit for my jobs, why?
This was very hard to debug among all the other errors that I was trying to fix.

If you want your users to be aware of walltime, isn't there a better solution than setting it to a random number?
Can't you make it a required variable?
Can't the default value be something like `"not-set-by-user"` and complain if it's not set?