End Of Prophethood
Earlier all the prophets except Prophet Muhammad pbuh were sent mainly to their own people (Moses to people of Israel, etc). PLUS the instructions/books given to them were after their death either fabricated or lost. Prophet Muhammad pbuh on the other hand was NOT sent to a particular community or nation or a group of people but to humanity at large. Secondly, the message revealed to him in the form of the Quran will be preserved till the end of time as promised by Allah. Thus, the final reminder and everlasting message has been sent by Allah and Thus, there arise no need for further Prophets or instruction (books) to appear, since we have the final frameworks and instruction with Prophet Muhammad pbuh and the Quran.