Sale and Leaseback FV Revaluation

Hi, please can you help address a question that occurred to me. When we account for a sale a leaseback at FV. Why is it that we want the right of use asset recognised as a proportion of the original carrying value. Why don’t we revalue the initial carrying value up to FV first, and then ultimately recognise the right of use asset at the same amount as the liability? Sorry if I’ve missed something obvious.

Thanks,
Anton