Your question relies on a slew of presumptions; that Germany was a great military power and all its allies were the ones that couldn't carry their weight, and the supposition that Germany fighting the majority of the world's armies was somehow not an outcome of its own making. Lets unravel this.

Lets tackle the easy stuff first, that Germany just....found itself up against the world's militaries, somehow. Germany's military opponents in the first world war were very much of its own making through decades of an aggressive foreign policy pursued by Keiser Wilhelm II after the dismissal of Chancellor Bismarck. Stressing for Germany's "Place in the Sun", German foreign policy went on to antagonize French colonial interests in Morocco, lock Germany into a naval arms race with Great Britain, and ensure military security against the Russian Empire with Austria-Hungary. You can read up on how Germany's aggressive approach to foreign policy was the catalyst for the formation of the Triple Entente in this answer of mine over here.

German wartime diplomacy during World War I also did the Empire no favors, with the German Navy's policy of unrestricted submarine warfare refusing to distinguish between neutral and belligerent when it came to shipping within proximity of the British Isles. The sinking of the Lusitania in particular created a diplomatic crisis that would have found the United States well within its rights to find the death of American civilians on a civilian passenger liner as an act of war. Ultimately, war was averted as Germany agreed to lift its policy of unrestricted warfare. However, Germany reintroduced the policy in 1917, as well as the interception of the Zimmerman Telegram, a diplomatic cable from German Foreign Affairs Minister, Arthur Zimmerman, proposing for Mexico to attack the United States was a naked act of aggression against a neutral power that couldn't be ignored, compelling the United States to enter the war against Germany.

In short, the German Empire found itself at war with so many military powers because of aggressive and militaristic diplomacy, which afforded them little love on the world stage.

Now when it comes to Nazi Germany, the foreign relations of the state was nakedly combatant. Aside from a tripartite pact with Italy and Japan, German foreign policy was primarily driven by launching wars of aggression against all their neighbors for territorial expansion, dishonoring or betraying almost every treaty it signed with foreign powers, forcing entire populations in its occupied territories into slave labor programs, and systematically murdering everyone the state deemed unfit to live. Germany found the world as its enemy because the state made the world its enemy, and the Third Reich has no other force to blame but itself for the enemies they made over the history of its regime.

As for the strength of its allies, throwing Germany's allies under the bus for not pulling their weight in the war is a common talking point of German generals in the post war, but it wasn't like Germany was doing any favors for its allies to support them either. I address over here Germany's failures not only to provide much of anything in the way of aid to their allies, but how they kneecapped their effectiveness by extracting any material wealth out of them to serve their own purposes., I also go over Germany's own military failures in this recent answer over here, where Germany has itself to blame for its military failures, brought on by the same supply and logistics failures that plagued Italy and Japan through the war as well.