A few things for me.
It's my money.
$50 USD is such an inconsequential amount of money that it makes no difference.
Its a prebuy of something i would buy anyways.
I get some immediate rewards that i will use prior to the expansion coming out.
It's my money.
Blizzard has yet to personally disappoint me, and Legion was so much fun that i will happily support Blizzard again, if Legion was WOD 2.0, i might be more hesitant.
To make OP madder, im actually getting the digital copy of the normal version, and the physical copy of the collector's edition. Again, the money is inconsequential for the extra time to level an Allied Race and pick a main for BFA.
It's my money.
If this was a game from EA/Ubisoft (i wont even buy a single title from that trashtier studio)/Gearbox i would not preorder it, but this is from one of the only studios to basically never disappoint me. I will wholly support Blizzard in their games until such a time as they radically disappoint me as a player.