The obvious is just that, while the final report, with all the detail, has to be compiled then passed to the consultant for review. And that isn't just a rubber stamping exercise: every scan has to be signed off, and often the experience of the consultant will bear fruit.
Sadly, that means the report is sitting in two In-Trays while overworked (and underpaid) NHS staff wade through them.
Of course it's frustrating. But I'm pretty sure they aren't doing it just to spite you!