I think it's important to distinguish between two very different things:
orchestral music as an art form
orchestral music as an industry
As an art form, I think it is very important for people to always be experimenting with new ideas, and I always encourage them to do so, even if the end result is something I don't personally like (e.g. Schoenberg, et al.) Who knows, maybe the experimentation may eventually lead to something exciting, or may encourage someone else to discover something interesting. As long as someone considers their art form an expression of something meaningful to them, I can't fault them as an artist. (Even if I don't like what they make).
As an industry, however, is another matter completely. Lately it seems like I keep seeing articles pop up about the "classical music world" that come in two varieties:
"Oh no, orchestras are going bankrupt, concert attendance continues to decline, why is this, what do we do???"
"Oh no, the public doesn't 'understand' contemporary classical music, why not, how do we educate them???"
My immediate thought is that the former is a direct result of the latter. It's not that they don't understand it, it's that they don't like it. And since they don't like it, they don't show up to concerts. You shouldn't have to educate someone on why your product is good, it should be apparent.
Furthermore, I don't think the "public" isn't interested in orchestral music. Concerts by Mozart, Beethoven, Tchaikovsky, and even those less-"household" names like Rachmaninoff, Stravinsky, Mahler are regularly well attended, at least where I am. And I'll go even further and say the "public" is even interested in hearing orchestral music by living composers. My local orchestra regularly puts on concerts of John Williams scores (Star Wars, Harry Potter, etc.), and those concerts SELL OUT. (I'm sure we could debate John Williams music ad nauseum, but that is a topic for another thread. My point is that people are willing to buy tickets to see orchestral music by a living composer, which defeats the belief that the public is not interested in contemporary orchestral music.)
To answer OP's question: I think the lack of financial success of contemporary classical music is due to a failure to give the people what they want and are willing to pay for. This doesn't necessarily make it bad art per se, but it isn't something you should expect to build an industry on. It seems like for whatever reason academia has aligned itself with training composers to write a certain kind of music, and the orchestras have aligned themselves with championing this certain kind of music, but most people don't seem to have any interest in paying to hear this certain kind of music. Thus, we are in the predicament that we are in...
I will offer a glimmer of hope: I think in the year 2020 it is easier than it has ever been to write and produce orchestral music (or chamber, vocal, etc.) and it will only get easier. Through most of history, most composers that rose to prominence did so through some kind of "connections", either through knowing someone in the industry, or through getting into an elite conservatory that connected them with big names in the industry, or simply by being born into a prominent musical family, etc. Now more than ever, it is easier for your average Joe to get their hands on notation software, DAWs, sample libraries, etc. Any information about theory, harmony, counterpoint, orchestration, etc. is easily available online. Websites like this one exist for composers to meet, collaborate, and share ideas. And there are many accessible platforms like YouTube, Soundcloud, etc. for getting music out to an audience. Maybe all this will lead to a new avenue, separate from the traditional conservatory route, for composers to get their music heard. I at least hope it does.