They will find out what you look like eventually, why waste their time and yours when you know it's inevitable? Is a 2 day text conversation the most relationship you can get?  I think they do it because they figure you would never give them a chance if you knew right off the bat that they were obese, but once you have talked to them a bit online or over text or whatever, you'd be willing to look past the discrepancy because you've already fallen for their "wonderful personality". When in reality, fatfishing actually showcases what a horrible person they are because they think they can build a relationship on a foundation of lies and manipulation.