If they order to collect someone's data, can't ProtonMail just say "we've been ordered to collect data for a user" on the front page?
Sure, ProtonMail and its current operators could opt to stop operating in such jurisdictions, but usually it's too late for that when you get the [secret] court order, because if you refuse the operators personally are quickly found in contempt of court (or whatever other bad legal circumstance), and eventually that can lead to similar InterPol/EuroPol (other MLAT) warrants.