SoftBank is the $100B vision fund. $100M is just 1/1000 of that. This is like if you'd own $100k and invest 100$ in something, that's not even worth a news.
$100 million is still $100 million, and what you can do with even less than that is not the same as what you can do with 1 billion.
Somethings in life don't make sense to compare to ratios.
The absolute amount is tiny but it surprises me that they haven't spent that amount in every major city. Surely there is at least one city out there that has promise and SoftBank would be the one with the first dibs.