You'd have better success getting people to fight for your cause when you provide them something of value they can't get elsewhere.

When what people get (using their labor to subsidize politicians & boomers via taxes & rent) is the same thing they can get in effectively any country or even under the invader's rule, the incentives to fight said invader become quite scarce.

This isn't even specific to Germany; a lot of people are fleeing conscription on both sides of the current conflict for the same reason - they just don't get enough benefit to make it worth putting their life on the line.