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Because many people are afraid of what is not familiar, that's it. It's not hostility, but a rather a case of shying away from reading the docs and changing the way they work. From my experience not everyone is conductive to try and adapt to new ways, and many people do not use git CLI or SSH. They just use GitHub's gh CLI command.
Believe it or not, there are people out there who don't care about decentralization and latency-tolerant store-forward networking for their own sake. Getting things done is way more important to them and the user experience of git send-email is simply not as good as the centralized version.