Chronos; that is the most simple answer. It is time that divides our attention the most. That includes your audience. As someone who does not much care about “building” an audience through schemes or tricks but rather talent alone, I have come to certain conclusions. One of the most important ones is that your audience’s time is valuable.
As an artist there are a number of media forms to work with. For the pure visual artist, you can gain popularity by taking up a moment of someones time. It is rather rare today to have someone spend intimate time with a single piece of artwork. Be that as it may, this truth has it’s own vices. It means the appreciation of your work is masked by numbers and the connection to your audience is loosely based around said moment. The good news is that your work is easily shared and enjoyed by a large swaft of people with minimal effort from your audience.
Then you get into things like music. It can be enjoyed on it’s own, or during something else. It reaches the soul and perhaps your work becomes someone’s theme; for a day or maybe longer. However, you capture your audience with an intimacy I would argue is far stronger than a visual art. A good space to grow in too because multitasking allows someone to hear your song. If you attract special attention with your talent you may even get them to say “Who made that?” and they will look you up. Download your music, maybe flash your bandcamp or soundcloud.
Similarly is the art of Podcasting or making youtube commentary videos. I find myself enjoying a large number of these kinds of media. All I have to do is listen while I do other more pressing things. It is easy entertainment. In that it also requires little time from your audience.
So if you see where I am going… movies, television, animation, to some extent require a greater level of attention. Now one can spend their time doing other things but at that point, they are missing a piece of the art itself. This requires a fair bit more attention and thus it is harder to build in audience in such media. Bad news for you film makers. However at that same time, I believe film can reach people in ways other forms of art cannot. This is because they will spend more time and attention with it. It makes it more personal.
Then you have the written word. Oh, I woefully inform you, the task of building your audience will be much harder. In order to build an audience in this field of art you must captivate them rather quickly. If you don’t you will loose your chance. See the thing about the written word is it requires not only all of your attention but it also requires a fair bit more of your time. So building your audience writers is going to be difficult to say the least.
At that same time it is an absolute treasure in reaching deep into someone. The written word can not only bring out emotion unlike other media types but it can truly seat itself. The art of making a reader walk through someone else’s skin for several hours is truly an intimate thing. It gives the reader a view of your inner mind. This is why writer’s audiences tend to be so loyal. You have spent a great deal of time with them.
Basically what I am suggesting is time + attention = audience growth difficulty. If you require time and attention it is harder. The more time you require the more difficult it will be, likewise with attention. So make it count, that is what you are up against. At this time it also means you are getting closer to your audience. The more time and attention they give to your work the closer the bond between you and them will be.