Really? It didn’t come with my boxed collector’s edition of Mists of Panderia.
You don’t have to have any authenticator, but Blizzard is pushing the idea because so many people got their accounts hacked in the past.
I, too, have been playing 7 years and never hacked, but then, we never bought gold or levels or items, and we practice good security on our computers in general.
The reason they push the mobile app version of the authenticator is due to player base demand, apparently that is the more popular option these days, but you can still get the stand-alone fob authenticators.
Hackers strip accounts of pixelated items, many of which are one-time quest rewards or hard to earn epics which may or may not be restored. Hackers also employ cheats in-game that can deprive honest players of game resources. Back in the day when Felwood was a zone used to gather high-end resources needed in raids you’d often see obvious bots employing cheats - on PvP servers folks used to enjoy killing them. Hackers of this sort also distort the in-game economy when they liquidate items on the auction house. If a hacker scores an account with a major guild officer or leader they can really screw with it, from selling off the contents to kicking all the members of the guild out and then selling the guild to someone else.
It’s a bit more annoying than “can’t get on line and spend my gold”.