ible
professional vim user
At least two reasons.
1. To keep the Fn layer symbol sets from the right side of a standard US English keyboard contiguous and over/under shifted/unshifted.
2. To keep the seemingly "weird/offensive" to some German symbols grouped together so they do not distract.
3. because the German a, u, o umlauts are over on the right side of a German keyboard. i claim part responsibility for putting this in the Pyra in this way, but it also freed up the left Fn keys to be more intelligently grouped, as Grench mentioned. a, o, and u are all over the place...