Because the articles of confederation were not working well for them. So they went federal.
The reason that the Founding States made the federal constitution was to limit (cripple) the federal government's powers.
And the reason that many patriots get zealous about supporting a particular person for president, the so-called most powerful office in the land, is because generations of parents have not been making sure that their children are being taught the constitutionally limited powers of Congress and the Oval Office.
In fact, it can be argued that one of the very few constitutional powers that the feds have to regulate anything within a state's borders is to regulate postal services as evidenced by the Constitution's Clause 7 of Section 8 of Article I.
And since the president and federal senators were originally not elected by popular vote, ideally citizens would now have to guess who current president is. Otherwise, if they don't like the way that the postal service is being run, they can complain to their elected lawmakers in the House of Representatives.
In other words, most of the government powers that Congress and the Oval Office now exercise are actually 10th Amendment protected state powers which corrupt federal lawmakers have wrongly stolen from the states as the Founding Fathers had feared.
Again, it doesn't help matters when parents don't make sure that their children are taught the federal government's constitutionally limited powers.