I'd assume singing was much more ubiquitous in the past, since it was one of the few ways ordinary people could entertain themselves/each other (this was clearly the case well into the 1900s in most, if not all, Western societies).
What changed was the mentality, how the average person related too music. Before the romantic era most people could not afford any instrument beyond a folk instrument and certainly could not afford lessons or time to dedicate to practicing. So singing may have come out of going to church and people so inclined would sing as they went about their day but they would not sit down with some sheet music and practice, that was for the well off. Folk instruments tended to be fairly limited in what they could do and did not require much in training or practice although some people have taken these simple instrument to great extremes and done wonderful things with them.
During the romantic era we had the rising middle class with more freetime and money to spare and all those musicians eager to have some more income from giving lessons. The composers started writing lesson books and methods suited to the amateur and the luthiers started building instruments for them including variations like the Decacorde by Carulli and La Cote [0] which was meant to be an easy instrument for the amateur.
Should mention, with "romantic era" I am not really referring to the literal era but the school and tradition of the romantic guitar as the dominant school which goes until the Spanish guitar and Western steel string took over around the turn of the 20th give or take depending on where you are in the world and how you want to look at things. The romantic school still exists to this day, the parlor guitar is a romantic guitar in everything but name and the Viennese guitar is still going in parts of Europe.
