I gave this answer to a very similar question before and went looking for it, only to learn that my answer was collapsed. I have no idea why. So maybe this one will also be collapsed, but I think it’s a good answer. Here’s my take on why balloons became a big deal for events.
Balloons have existed in various forms for a very long time. The first rubber balloons appeared in the early 1800s, and mention of other types of balloons were found in literature before that. I’m not sure what metric we should use to determine the point that they became popular for decor, so I’m going to pick the late 1980s. It was at that time that there was a critical mass of professionals using balloons that the first professional balloon art conventions started appearing. So clearly there was demand for it. And of course, once you had organizations and conventions forming around balloon art, the popularity could grow at a much more rapid rate.
Because birthday balloons are cheap and colorful, children like to buy them and play with them. Balloons were first used for scientific experiments and transportation, but they soon found their way into people’s hands as a tool for entertainment.
My oldest son is now 21 years old and still loves balloons very much. He plays with them like a child and it’s a lot of fun. Whenever I can, I buy him balloons all the time at https://balloons.online/licensed-mylar-and-foil-balloons/ . He likes balloons with different designs, so I buy him different ones all the time. He gets excited about them and it makes me feel good.