ActiveMQ Performance with number of destination

Hi,

Using ActiveMQ 5.8

I was doing a performance test for ActiveMQ with increasing number of
destination(both topic as well as queue). Below is the behavior I observed:

Test: Previously all the msgs were send to a single destination, now by
increasing destination those messages are redistribute among all
destinations.

Expectation: Throughput(messages/second) should increase. Since previously
msgs are send on a single destination. Now distributed among lot of
destinations.

Observation: Throughput(messages/second) is almost constant.

Not able to understand. Why throughput is constant ?

Thanks,
Anuj