Well that raises two important points. Those being means and motivation.

Simply put it was not exactly simple getting out of Germany in Spring 1945. The most likely way, by U-Boat was still incredibly dangerous, requiring special provisions to be made on only the longest ranged ocean going boats. And even then would have required any party to get to first a base in Germany, say Kiel or Wilhelmshaven, which were under easy air attack by the Allies. And from there perhaps to a slightly more secure base in a Norwegian Fjord for final preparations. And then past Allied aerial patrols, surface task forces, and hope intelligence about such a transit had not been found out and hunter killer task forces had not been sent along the route.

And once into the Atlantic the question would be where to go. Japanese bases in the Dutch East Indies were being reduced or taken back one by one thanks to surging British effort that had pushed Japan from the borders of India. The Indian Ocean was now much more heavily populated by British and Allied ships and aircraft which could threaten the journey. Penang on the Malay Peninsula had served as the operational base of those German boats sent that far, but the island and town had been subject to heavy bombardment and naval mines placed to hamper Japanese shipping.

Singapore would be slightly safer, but is still not Japan, and by a subs arrival in Summer of 1945 would have virtually no ability to aid it on its journey. Allied raids, lack of ability to repair ships, and attrition had rendered the Japanese Navy virtually defunct. What ships were left were basically reserved for one way trips, or desperate attempts to get supplies back to the Home Islands. And at that through an ever tightening ring of Allied subs, patrol aircraft, and naval mines. Subs had made the journey often enough in earlier points in the war, though it was never common, but now that virtually all safe harbors had been removed between Japan itself and the German homeland the difficulties were much increased.

To say nothing of Nazi leadership's willingness to even consider it. Hitler by the end has resolved to die in final conflagration in Berlin, refusing even attempts to fall back into any final fortresses in German held territory. To attempt to flee towards a nation that he had never been a particular friend to, nor they to him beyond convenience, would have been a complete break in Hitler's previous positions.