Really? I fail to find a distinction between them. For design purposes, there is no difference. Threading hardware, for manufacture, is available for both in the US, and both are available, although some localities offer less of one or the other.

What's simpler about metric?

And did you read the thread a few months ago from the guy who had an Italian item with a metric thread he could not obtain (I forget if it was a 7mm item, or an M 0.7 thread, but he could not obtain it, and I couldn't find it on the Web.)

Anyway, good luck,
Dave Olson