Someone with a HotMail account has managed to keep a consistent address for about twenty years. That is a good thing. The idea that they should ditch HotMail for the functionally equivalent GMail just because GMail is popular is, of course, idiotic.
But this is an insurance company, so it is plausible that they crunched the numbers and found a real effect.
I still log into my old Hotmail account every few months just to keep it from getting deleted. It’s a complete piece of shit, it’s not even usable let alone comparable in any way to gmail.
For historical reasons, in case there were ever some account on some rarely used service where I forgot to change the email, and in case I ever need to build something on the MS Graph API.
But this is an insurance company, so it is plausible that they crunched the numbers and found a real effect.