Hi
2 things .... ( or 3..)
1. Historical ... typewriter -> electric typewriter -> keyboard, because...
2. bigger costs more to make (especially when iron), and originally made for female clerical staff.
3. How would such spacing work on an ANSI style board? Especially the inner columns, or outer edges.
I also find 19mm a bit cramped, and don't have particularly large hands.
Cheers, Ian