The idea of God having a personal name, is mainly owed to the hebrew cultural surrounding in the phase of development of jewish religion, it was a polytheistic surrounding. A name served back then as a distinction to other gods. The proper name expressed the attributes of this godhead is a second factor, the name YHWY doesnt only make it addressable but garantueed a certain closeness of God to his people. The event of the burning bush with the revelation of the name became the saga, which expresses the thought that God is merciful.
The loss of the original pronunciation is owed to an inner jewish process. Using the proper name today would be the same like celebrating again the polytheism and going back to a time when names distinced gods like in old Israel.The loss of the pronuncation is not due to a loss of attentiveness but a widening of the concept of god to a universal god.
The jewish community has in the course of the time become aware of the fact that there is only one God for all men and therefore supported that the personal name got less important. If this already began happening during the time when Israel was dispersed and in babylonian captivity is possible. When the hebrew scripture were translated into greek in the 2nd century before christ already "Kyrios" had replaced the proper name in the jewish world, also in the Qumran spricpures the personal name was replaced with "El", God.