@underlap content migration has historically been a difficult problem to solve simply because all these companies and softwares operate in pseudo-competition with one another.
For example #nodebb can migrate posts from #phpBB#vBulletin etc., but it's all custom migrators.
Something as simple as a common format for data portability would go a long way towards ease of content migration.
I am not certain many users elect to use or not use platforms based on portability though.