Question

Why was the Reapportionment Act of 1929 passed?

Answer 1

The answer for this question is that congressional districts were redrawn to establish safe seats for the political parties. 
Before the Reapportionment Act of 1929, the Republicans tried to take over the presidency and both houses of Congress, so that rule would be solely through the Republicans and that no Democrat would have any say over how to govern America. 

Answer 2

The number of senators per state was changing as the country expanded, it was limited to two representatives per state.  Congressional districts were redrawn to establish safe seats for the political parties.  Membership in the House needed to be capped to prevent an excessive number of members.