Anecdote, but this past year, some new experience with a few people showed me part of the apparent reason for the dominance of Messenger: Discovery.
You meet someone. You want to follow up with them, for whatever reason. Most people have a public enough profile on Facebook that Messenger is the obvious answer. And, like Facebook, "everyone" is on it. Even if they conduct their more personal and intimate social media interaction on other platforms. To "reach out and touch someone", ping them on FB/Messenger.
Not saying I like giving FB that position. But, they currently appear to indeed have and dominate it.
P.S. A frequent circumstance is a friend or acquaintance of a friend or a coworker. Someone at a party. Etc. Your respective social graphs are already grazing if not overlapping, so connecting the dots on FB is trivial.
You meet someone. You want to follow up with them, for whatever reason. Most people have a public enough profile on Facebook that Messenger is the obvious answer. And, like Facebook, "everyone" is on it. Even if they conduct their more personal and intimate social media interaction on other platforms. To "reach out and touch someone", ping them on FB/Messenger.
Not saying I like giving FB that position. But, they currently appear to indeed have and dominate it.
P.S. A frequent circumstance is a friend or acquaintance of a friend or a coworker. Someone at a party. Etc. Your respective social graphs are already grazing if not overlapping, so connecting the dots on FB is trivial.