Is there a special reason for this?
Marcus, there are another reason too:
from some time ago, our regulators (in U-, R-lands) decided not to prolong old callsign, if license holder will be forget to re-new license before end of the current license valid period (every 3 or 5 years).
So even if we forget to prolong license not less than 1 month before end of issue, regulators will be not re-validate our callsign, even if we held it well for many years!
They will issue a new "next free in their database" callsign! Its really stupid and pity!