They are free to play because they have a cash shop for everything, so you can opt to play in and not spend, but tons of players still spend money.
Cash shop is industry standard for free to play, and with a 14 year old realm, getting bis gear with cash shop is probably less than 1 or 2 ticket run gdkps
I’m sure blizzard would love a cash shop for a game they don’t have to invest any money on fixing or changing anymore, just keeping 1 eternal realm and one seasonal wrath realm that transfers end of phase chars to eternal realm then starts another fresh round for those fresh enjoyers, if not they are literally giving up money they could be making that someone else is making off them.