Most of these troops, if not all, were locked in place. Most of them were second or even third rate garrison forces, or severely depleted, cut off and hemmed in.

Lets examine some of them.

The German troops in Norway numbered some 400 000 when the war ended. However, only about 100 000 of those were actual combat troops. The others were mechanics, cooks, clerks construction troops, ground crews, naval maintenance personell, logistics troops and so on. By the end of the war, the Germans had based much of what remained of their navy and air force in Norway to keep them out of harms way - the non-combat troops associated with those arms followed, and made up much of the troops stationed in Norway. Much of the 100 000 combat troops were made up of second rate garrison formations that lacked the prime movers to move their heavy weapons and the supply train to keep them on the move. The only high-quality troops in Norway were the mountain troops that had been part of the 20. Gebirgs-armee in northern Finland and had retreated from there to Norway during Autumn and Winter 1944-45. The Germans had been taking their best trained, equipped and experienced troops out of Norway for the last two years, and by the time Berlin was threatened, most of the troops there would have been nothing but a slight speed bump for the Red Army. And even if the Germans had wanted to move troops, by Spring 1945 they lacked both the coal to move large amounts of troops from northern Norway to southern Norway and the fuel to transport them from the southern Norwegian ports to Germany proper aboard German ships. Not even speaking on how the British and American navies and air forces had started dominating the North Sea and how dangerous such a journey would be.

The German Courland Pocket, in southern Latvia, contained what remained of Army Group North, which had been surrounded there by Operationbn Bagration Summer-Autumn 1944. The Germans had maintained these troops there as a way to threaten breakout and bind significant Soviet forces to their containment. The Soviets were content to hem them in and ensure they went nowhere when they were marching westwards. Rougjhy 200 000 men were in the pocket. As with Norway, by the time Berlin was threatened, the Germans lacked the naval lift capacity and the fuel to keep it going to evacuate the pocket.

The Germans also held many of the ports along the French coast - these were held by second or third rate garrison troops that were nevertheless well supplied and extremely heavily fortified. The Germans took the decision to retain these ports and order their garrisons to continue to fight to deny them to the Allies as they advanced across France in Autumn 1944 - the basic idea was that denying the ports ot the Allies would eventually make the Allied situation in France untenable due to a lack of supplies and that Germany would eventually recapture France and force the Allies out. The port garrisons were surrounded and under siege and could go nowhere to help other than to hold their own ports.

The German troops in Austria were an amalgation of German troops that had fought in the Balkans, both of Army Group South and the occupation forces that had fought Tito's partisans in Yugoslavia and occupied Greece and the forces that had fought the Allies in northern Italy. They had their own enemies that were pressing hard on them and were thus unable to go anywhere.

Germany did not have a lack of troops in Spring 1945, actually. The Allies took roughly 5 000 000 German prisoners during 1945 - of course, a lot of them were rear area troops (such as those mentioned in Norway) disarmed after the German surrender, and the Soviets took about 1 000 000 of their own. The Germans lacked heavy weapons, ammunition, fuel, tanks, prime movers, supply and food, not men in uniform in 1945.

As for why the situation was as it was in 1945, one needs to remember that depsite the devastating losses the Germans had suffered during 1944, in Autumn they stabilised the situation. The Americans got stuck in the Hurtgen forest, Operation Market-Garden failed and sent the British back again. The Germans continued to hold the French ports and the north bank of the Scheldt estatuary, meaning the Allies could not use Antwerp (one of Europe's biggest ports), casuing massive supply issues. At the same time, the Germans halted the Soviet advance in the east in October. To some in the German leadership, it looked like the situation might actually be reversible, and that the troops held in various positions could be used as a springboard for future offensives.

By the time the Soviets were nearing Berlin, the German ability to move large amount of troops had completely collapsed - the lack of fuel and ships made any seaborne movement of troops impossible, not even speaking of Soviet submarines - the last effort to evacuate as many as possible from East Prussia and Königsberg in January 1945 pretty much ended both the German navy and their merchant marine. In March 1945, the German railroad network finally collapsed tue to a lack of coal and extremely vigilant Allied air attacks.

So, to answer your question.

1. Those troops were mostly second rate garrisons at best and would be of little use.

2. The Germans had lots of poorly equipped and supplied troops in Germany already, a few more would not make much of a difference.

3. When the Germans actually had the ability to move some of these troops to central Germany, they had just stopped both the Allies and the Soviets and had some hopes that they could reverse the situation and those troops and the land the occupied could either be used as bargaining chips or as springboard for counter-offensives.

4. Once the Germans were in such a desperate situation that they could have needed those troops, their ability to conduct large-scale troops movements had ceased completely due to the collapse of fuel and coal supply and the complete collapse of the German railroad network.