The EU didn’t make it particularly hard, they actually were way too lenient and made quite a number of concessions, mostly in order to not escalate the Northern Ireland situation.
It was the UK that kept insisting on renegotiating the Withdrawal Agreement over and over again, and the EU was lenient enough to let them have their way whenever they asked for renegotiation.
But the German unions are mostly happy with the status quo and are doing nothing to challenge it, because most union leaders also get to sit on the boards of the companies they are supposed to represent their members against, and have a cushy revolving door with the “Social” Democrat party.
They also keep massively underdelivering in the narrow field where they can act legally, most often not even securing enough pay raises to compensate for inflation. This has lead to a vicious cycle of weak unions losing members due to their weakness and becoming even weaker.
They are doing the entire workers’ rights movement a great injustice, especially considering that unions and strikes were entirely illegal in the past and many people died fighting for making them legal.