There is perhaps a benefit to having several mutually unintelligible languages all "sort of" compile back to the same written text, but that benefit is increasingly being eroded as the version of Mandarin spoken in mainland China becomes the lingua franca, not just inside China but also in parts of the diaspora.
If everyone is more-or-less able to understand spoken Mandarin, then it's no big leap to codify a phonetic written representation of that pronunciation, whether using Zhuyin or Pinyin or something else. It's a totally achievable goal, and we know it's achievable because Vietnam, Korea and Japan already did it. Claiming it's impossible is just Chinese exceptionalism.
The real question is not whether it's possible, or whether it would make the language easier to learn, it's whether Chinese-speaking people - and in particular the government with an authoritarian rule over the education of the overwhelming majority of Chinese-speaking people - want to do it. And the answer is they do not. And so it persists.