Purchasing Bitcoin legally is a pain. If you have an online bank account, most of them do not allow cryptocurrency purchases via debit or credit. Even some traditional banks will not allow cryptocurrency purchases via debit or credit. If you have to go the route of bank transfers, you'll have to pay transfer fees and sit through 1 - 3 days of BTC price fluctuations. If you want to use cash or bank deposits via LocalBitcoins, you'll be paying a significant markup over Bitcoin's trading price, and most sellers have a KYC policy that would allow them to easily steal your identity.
Say you have a credit or debit card that can be used to buy cryptocurrency. Registering with an exchange is a hassle requiring a camera, a phone and multiple forms of photo ID. There is a waiting period before being allowed to purchase cryptocurrency. Exchange fees are high, as are transaction costs. I bought a small amount of BTC and wasn't allowed to transfer it from the exchange for 24 hours because of fraud protection.
I did the math and I would lose more than the 15% discount would have saved me just by buying and transacting with Bitcoin. On top of that, the entire process was unpleasant.