In addition to @fefe's answer, which correctly explains this very basic pronunciation rule, I'd suggest to search for videos in Standard Mandarin about 一举两得 and see how its pronunciation is invariably yìjúliǎngdé.
(His pronunciation is yìjúliǎngdé, 4-2-3h-2)
In the video, the man repeats 一举两得 four times. For your convenience, I cut out those small ...
It's very convenient to pronounce two consecutive third tone 3-3 as 2-3. A simple example is 你好. I have to make a clear effort to make "nǐ hǎo". But "ní hǎo" comes pretty naturally and fast from my mouth.
This might be regional where people could make a easier "nǐ hǎo" than "ní hǎo".
Anyway, my point is that if you ...
Q1. "Why are there two standards?"
According to Wikipedia (https://simple.wikipedia.org/wiki/Zhuyin) , Zhuyin was the first phonetic system in use from 1911 after the xinhai revolution.
After the overthrow of China's last emperor during the Xinhai Revolution in 1911, the new government in China created Zhuyin to help the common people read ...