Everyday there is a new cryptocurrency that’s “going to be the next big thing”. Investors rush to buy it and the price shoots up, spurring more interest, which leads to more investment, and the cycle continues until there’s no one left to buy in. At that point maybe bubble pops, or maybe it coasts, but it doesn’t really matter - there will be a new next-big-thing tomorrow. When people rush to the cryptocurrency exchanges to buy whatever the crypto du jour is, they first have to get the funds to pay for it.
Now that you have a wallet setup you’re going to need to actually get some bitcoins into it. There are many ways to purchase bitcoins, but none are as easy as could be hoped. There is no website you can go to and use your credit card and immediately get some bitcoins in return at market value (which is whatever Bitcoin is selling for on the exchanges). If you want to buy bitcoins cheaply (or at least, at the fair market value), you’ll have to use one of the currency exchanges.