As sports betting legality expands across the country, more sites will continue to add PayPal to their list of accepted payment methods. DraftKings and FanDuel are at the top of the list because they already had deals in place with PayPal while offering Daily Fantasy Sports.
That said, most other sports betting sites accept PayPal and if they don't, that'll likely change in the future. Other popular operators like bet365, BetRivers and William Hill also allow deposits and withdrawals through PayPal.
PayPal withdrawals are sometimes only allowed at sites after you make a deposit with your PayPal account. As long as you have a balance in your PayPal account, there are no fees if you deposit to an online sportsbook. That's the main bonus for using PayPal because if you're depositing a decent amount of money, most sites will charge a fee for using a credit card.