I am not worried about a 1% edge case
When I worked, we used to have to often change room types from rooms with 1 queen bed to a room with 2 full XL beds (full XL is 6 inches narrower than a queen).
Of course, technically, this would modify a guest’s reservation and give them an inferior bed than the one they reserved, so we would go down the list of people who had reserved a room with 1 queen bed and ask if they were willing to change to a room with 2 full XL size beds, and as a thank you, offered a few thousand points.
Obviously, all the single business travelers had no problem accepting a couple extra thousand points for a bed that was 6 less inches wide, but if they did not have a good phone number on the reservation, they were not offered.
Much like the person that has their 2FA app on their phone, and their backup keys burn down in their house and then is suddenly on HN begging for Google support to help them because they are in a catch-22 situation no one cares about the edge cases until they are being crushed under one.
Also a 1% failure rate is off the charts when you're talking about serving millions.
/s
At franchised hotels in the US, which is almost all chain hotels, the employees at the front desk do not have the ability to email you, or even know your email address. The phone number is often the only way to reach you.
Hilton does have the chat app, but I do not think it works for hotels trying to reach customers with time sensitive information.