I think, for some, it's because they gift or sell the soap later and prefer to keep it untouched. I've actually heard someone claim it in a video reviewing soaps.
Me personally, I have been experimenting between loading from the soap with a brush and scooping into a dish then lathering. Trying to find the best lather. FYI, it seems to be a wash. So long as you take the time, either way, to get enough soap in the mix, it works well.
I also use my spoon to mix soaps... Twice only, so far, but it's still useful. [emoji16]
I have used spoons too.
I have a Swix cross country ski wax scraper that is perfect for the job.
Your local hardware or woodworking stores are likely to have a scraper or grout tool that would work fine.