According to Wookiepedia, few organics have directly learnt and understood Binary, and these are mainly people who interact with droids frequently at a technical level, such as pilots, mechanics, scavengers etc. Even then, it tends to be people who develop an interest into taking up the language. It provides droids with an ability to speak vocally even though the recipient more often than not relies on a text display screen or a protocol droid for a comprehensible translation, often in a more organically natural language.
Clearly, Binary is not intended to be the standard language of communication between droids and organics. Where it is needed, language packs and compatible hardware for common languages such as Basic or Huttese are installed into droids. The main design intent of Binary is for droid-to-droid communcations.
Ignoring out-of-universe needs to portray communications to the viewers, what is the in-universe basis for Binary's existence in the first place?
- For droid-to-droid communications, wireless communications are faster, usable over any range where audio words work, is more secure (cannot be overheard, can be encrypted, etc.), and do not rely on the presence of a sound-transmitting medium. Vocal words are only useful when the droid is being jammed, which is probably a minor proportion of the time in droid-hours spent by the galaxy communicating. Inventing a language just for that seems impractical.
- For droid-to-organic communications, the preferred methods are already mentioned. Basic doesn't seem to be designed for this. Even if a droid that cannot speak organic languages needs to draw attention from an organic, there are easier means of doing that without going to the point of inventing a whole language. For example, loud noises in general or flashy lights (or a galactic Morse Code!). Basically, most people can't understand it to this day anyway.