At least that's what a linguist suggested to me when I lamented my inability to learn some foreign languages as well as peers.
Example: a circuit diagram. You have a transistor and some other components, and if you know the language you can recognise it as an emitter follower. It's a very concrete and clear mapping.
There aren't many things you can do with a transistor. When you've learned them all, that's basically it.
Human languages are much bigger. If you ignore the alphabet level and start with words, there are thousands of symbols (tens of thousands for advanced users). And most of language is about implication and context.
If a partner says "What time will you be back tonight?" that can mean anything from "Because my car is still in the garage, can I borrow your car?" to "Are you still having an affair?" to "Will you make it in time for curfew?"
In most conversations and a lot of writing, the words are hints, not explicit mappings to defined meanings. You can parse an immediate meaning without knowing the context, but not the full meaning.
So it's a much harder problem. You have to learn basic grammar and vocab for tens of thousands of symbols, then learn standard basic exchanges in social situations, then special forms, idioms and social register, then implication and subtext.