Why are online translators crap at capturing nuance?

I'm not talking about translations of basic dialog such as "How are you?" or "Nice to meet you." from English to let's say Japanese, Mandarin, French, Spanish & whatever. Rather the topic dwells more on translation apps or LLM's failing to capture the nuance of a conversation since words can connotate different definitions as well as being understood differently when applied.

Take the word 蛇行 (だこう) which is defined as amongst the lines of "meandering" but when compounded with 蛇行運転 for example, the definition leans closer to "erratic driving" but most online translatiors mess this up on saying "driving in a serpentine manner" which sounds stupid. No wonder why Japanese is hard for LLM's to work with.