The migration request has been declined due to the questions' age. Apparently, SuperUser has a moderator policy of not migrating questions older than two months.
Would it make sense to place an "official" request in the SuperUser Meta to allow for migrations of this kind if we explicitly ask for them? If so, what would a sensible procedure look like? For starters, we might discuss each migration candidate in SF Meta first to see if the majority agrees that it is a good fit and just raise a moderator flag referring to our meta post. This is rather heavyweight, but would prevent annoying SU moderators with migration requests of questions which would get closed here afterwards.
The rationale behind all this is increasing SF's weight in relevant areas through the aggregation of interesting content. People still asking on SuperUser about Puppet manifests and Munin plugin configurations might be a sign that we are not perceived as the right place to go for this kind of questions. And apparently SU moderation is either unable to tell these questions are on topic here or is too put off by our "we don't want (SU) crap here" policy to even try migrating these questions. Speaking of which, are we even on the migration target list over at SU's?