I find Wingard's reasoning for asking Junkie XL to do it perplexing as well.
"Well, the original music was meant to highlight the Japanese Godzilla and the tragedy around it, so we won't use it. But, can you make your theme sound like it?"
If you're going that far, then just use the original themes. McCreary proved that they can be updated faithfully. If you want original music, then do original music without having to make it sound like a bootleg of a past composer. I literally got told 'well, other composers in the franchise also didn't use Ifukube' when I expressed this. Yeah, but the key there is they wrote their own material that didn't sound like a rip-off. Takayuki Hattori, for example, came up with an entirely original score for the much-maligned Godzilla Earth trilogy. He wrote an entirely new theme for Godzilla. Not one note sounded like anything Ifukube wrote. Same goes for Michiru Ōshima, the composer of Godzilla Against Mechagodzilla and Tokyo SOS. And of course, as previously mentioned, Desplat's score for the 2014 film.