MS Migration Assistant (SSMA) index renamed
While there are reasons that a tool might make intelligent decisions about index names (like to prevent duplicate names in cases where there are actual collisions, and further when it actually matters, like when they are in the same table), it would appear that SSMA just creates new, unique names for all indexes. Perhaps only in the case where it finds at least one index name that is reused, not sure. I would test this, but I don't have Access installed anywhere.

Why does it do that? Who knows? Extreme conservatism? Paranoia? I think it's just being extremely safe.

There are cases where duplicate names would be a problem, but these are isolated to first class entities that end up in sys.objects, like primary key constraints. Index names are only enforced to be unique at the table level (since the name is only exposed in sys.indexes), not at the database level.