Entry Credits used to make entries into Factom blockchain. Buying EC is quite difficult for people and companies who want to try Factom. They need to register on cryptocurrency exchange, proceed KYC procedure, wait for approval, buy Bitcoins, then buy FCT (Factoids) and then convert it into EC.
EC Store simplifies buying Entry Credits — all you need is a credit card and existing EC wallet.
Sometimes local laws restrict companies to buy security tokens (like BTC/FCT) with corporate funding, and then there are 2 options for companies — don’t buy security tokens or use personal money instead of company’s account. Buying EC directly for fiat solves this problem.