YOU CAN SAY BECAUSE YOU ARE VERY FAR
Don't you think more the merrier. I mean we need as many prophets as possible for the guidance of humanity.
One thing is common among all the prophets that they declare themselves supreme authority. Prophet Muhammad PBUH said that he was last prophet, even Moses would follow him if he would come that day. Jesus made same kind of claim that he was the authority of the day.
One reason could be that they wanted to establish their writ and bring people in order. Today, that countries are not based on religions but economic systems, we can have as many prophets conveniently.
There will remain confusion unless we understand the concept of 'eternal religion' i.e. one god many paths. Islam, Christianity, Sikhisn, Budhism all lead to one Supreme Being. A person can be Hindu, Sikh or Muslim whatever he likes, ultimately he will be within the [braces] of Eternal Religion. It is easier today because human has achieved social order notwithstanding any religion.