a) jurisdiction dependent, it's a bigger company than the US.
b) if they issue RSU's at $Y, then buyback stock to drive the price up to $Z, the employee's take $Y as ordinary income, and $Z-$Y as cap gains, which is usually taxed more favourably
Mostly because they are used by party donors and other wealthy people who "influence" politicians. When everyone gets paid in dividends, they'll find different mechanism for the wealthy to extract money and tax dividends just like any other income.