[srfilipek]

Think about the different user bases and sources of revenue.

If google screws up, they might see a small blip in add revenue before recovering.

If Protonmail screws up, then they'll lose paying customers which is their only source (presumably) of revenue.

[joshuamorton]

I can't say for sure, but I'd guess that Gmail has many more paying customers than protonmail. This feature exists specifically for those paying (enterprise/gsuite) customers.