The short answer is Germany made them selves look so unattractive through their political and militarily dealings that all the other powers ended up making agreements with each other to counter the threat they saw in Germany.

Germany was coming off the period from 1871-1890 where Otto von Bismarck had set up agreements and treaties to keep the peace. The Austro-German Treaty of 1879, The League of Three Emperors 1873, the triple alliance of 1882, the reinsurance treaty of 1887 etc.

Then Wilhelm II kicked out Bismarck and started making aggressive plans. He declined to renew treaties such as the 1887 reinsurance treaty with Russia in 1890. Wilhelm has been said to have thought that his personal relationship with Alexander III of Russia would be enough. This also started a period where Germany really wanted to ally with the English. Which is odd because as of 1889 Wilhelm operating on the thesis that naval power was the key to dominance started rapidly building up his navy and starting an arms race with England.

This build up coupled with belligerent political actions mostly with the french who was still pissed about the Franco-Prussian War (Which i should have mentioned sooner as a major point of why at least the French wanted nothing do with Germany) would lead to series of Crisis centered around colonial possessions in Bosnia (1908) and Morocco (1905 &1911).

Would you trust Germany if you were France or Russia? That just leaves England who played it coy for a long time but after the Moroccan Crisis and in light of Germany's naval build up wasn't a fan either.

I recommend Norman Rich's work "Great Power Diplomacy: 1814-1914" as a good overview on the subject if you are still curious.