Costs, It all comes down to labour costs and this changed depending were you live.
From experience the floor type is much simpler and easier to do than a wheel arch one so if anyone can follows Hurdys step by step they can do the wheel well one just as easy. Infact its much easier do too less effects of gravity lol.
(Note: non of the above photos are ones i have done myself there ones i have saved to my computer to get ideas from in the past.)