yes, you are right there can be valid reasons for discontinuing work that does not result in a 3 week quarantine.
For example, you can refuse or terminate a job or offer without quarantine if you have the documentation of a doctor that the work gives you health problems. It is a requirement that you have tried to get another job at work.
If your transport time is more than 3 hours a day, you may decline an offer/stop work your self. In some cases, however, you must accept more than 3 hours of transport a day, for example if you live in a place where longer transport time is needed than usual.
Care of family
If you do not have childcare facilities or care facilities for other family members in need of care, you may refuse or terminate a job or offer without quarantine.
Spouses or cohabitants move to take over work
You can also terminate work without quarantine if your spouse or cohabitant moves to take over work of a duration of at least 5 weeks or start training (for more than 18 months) or commence self-employment for more than 30 hours a week.
You have found a job yourself
You can terminate a job if you want to take over another job of a duration of at least 5 weeks or start a study of more than 1 year duration or start a self-employment for more than 30 hours a week.
There are several other options for avoiding the quarantine. We recommend that you contact your A-kasse before terminating or refusing a job or offer and getting further guidance as the rules are many and complex.
Regardless of you having a valid reason, you still need to be available for taking over a full time job with 1 days notice, for being eligible for unemployment benefits.