1. Roth IRA doesn't have mandatory withdrawal at 70 1/2
In 401k and traditional IRA there is a mandatory withdraw rule at 70 1/2 years old. No such rule in Roth IRA so you can keep the money longer.
This is particularly true for high savers such as Chinese people.
2. tax rate advantage.
from 2018 to 2025, for eight years, income tax rate is lowered by the trump tax cut. After 2025 the tax cut expires. So from 2018 to 2025 is a good time to load up on Roth IRA because tax rate will go up in the future.