In cases like the Syrian civil war or political prosecution in regimes like Iran, it can easily be more than a decade. If you prohibit anyone from getting any work for that long and force them to sit on their hands (or work illegally without a permit), they will have a hard time getting back into work and probably continue to rely on government handouts. Who wants to employ someone who hasn’t worked any job for a decade (as an adult) after all?
So you have a choice: Either you allow and encourage refugees to get into the workforce early and accept that they will probably remain here even if they could return after like 5 years. Or you stop them from working for years and accept that many refugees will remain here for decades and rely on government handouts the entire time without ever finding a job.