They were designed for Alaskan''s to reach further in to the wilderness.
Then us non snow type people discovered they were awesome on sand, as long as you use dry lube on the drive train.
I've been riding fat bikes for almost 10 years (in November) now up here on the Merseyside coast.
About 4 years ago every bike manufacturer and his dog launched a fat bike, that then flooded the market with them, then that flooded the 2nd hand market with those who didn't really have a need for one and in a way killed off fat bikes growth here in the UK.
Not one mainstream manufacturer launched a fat bike this year they have all moved in to E bikes.
I love mine and while I can still get parts I will always ride them but try before you buy and look at the 2nd hand market for as new bikes out there