This question surely isn't appropriate to be asked neither on Stack Overflow nor on Super User. Why was it migrated to Super User instead of being closed?
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This is a combination of two issues.
First, migrations to X are decided on by people who know Y very well, but may not have any particular knowledge of X. This is exacerbated by the fact that it's majority rule: if two 3K+ on Y know it's not applicable to X, but three 3K+ mistakenly think it is applicable to X, it's going. There is no action available to anybody on X to refuse the migration.
Second, Super User does not have, and never has had, a coherent explicitly stated identity. Unlike sites for, say, programming-related questions and professional system administration questions, it's for hardware and software questions that don't fall into certain categories. I'm only moderately active on it, so I don't know how well it's developing a community identity, but any implicit or emergent identity is going to be lost on those voting to migrate questions to it.
And, no, I don't have a better idea, unless we alert Super User moderators of questions that may be migrated, and allow them to block migration somehow. That would complicate things considerably, increase the duties of the moderators, and potentially cause confusion among the closers.
Indeed, those with closing powers on SO should at least know this doesn't fit on SU either, and close appropriately (being off-topic).