Why did the daguerreotype process eventually decline in popularity?

There were two main reasons.

One is that people wanted numerous copies of a photo. Daguerreotype made photos on thing sheets of metal which were extremely easily damaged so glass had to go over it. There was no reproduction of photos and photos made were the only ones in existence unless numerous same photos were made with multiple pieces of metal.

Another was that paper made it better and more portable. When pictures started coming out on paper, it was much easier to carry it around and take pictures and print them on paper. The daguerreotype proved to be inefficient and too robust for the needs of the people as photography started developing more.