I agree with the posts so far, though that kind of denial of the importance of details applies to a lot of custom frames also. What is the role of the Fleur du Lis on the lugs kinda stuff. Or the lugs.
In general that kind of thing looks intended to soften the rear end, and harden the front end. Why that would appeal in this case could just come down to marketing hooks as mentioned. Or it can be that for some reason they tried it, and for whatever reson that particular bike worked great. Like going into a shop and riding three seemingly identical bikes, and yet one feels alive and the rest are like riding a section of guard rail.
Why a deeply ovalized and curved tube. Sorta nets out at higher weight.