X-Men from different realities are brought together to ensure continued existence for all realities. Gathered by the Time Broker and guided by the Tallus they are sent to 'correct' realities that have strayed, or will stray, from their respective time lines.
The Exiles are dumped in to a reality where there is zero tolerance for mutants and superbeings. They have all been jailed, executed or aborted. The Tallus only offers the instruction to find "The one who would lead us."