Mexicans have a strangle-hold over the Oscar for Best Director

I'm not much of an Oscar follower, so it came as something of a surprise to have pointed out to me that, if Alfonso Cuarón wins the Academy Award for Best Director this year, as seems more than likely, then Mexican directors will have won 5 of the last 6 Best Director awards:

• 2018-9: Alfonso Cuarón for Roma.
• 2017-8: Guillermo del Toro for The Shape of Water.
• 2015-6: Alejandro González Iñárritu for The Revenant.
• 2014-5: Alejandro González Iñárritu for Birdman.
• 2013-4: Alfonso Cuarón for Gravity.

All, obviously, very good films. The only non-Mexican interloper in recent years was Damien Chazelle for La La Land in 2016-7 (not in the same league at all, in my humble opinion).
What is in the water down there?