Why is it so hard to learn languages?

I have a B.sc in Mahtematics, still I have a hard time learning languages. Why is this?

Because you're autistic and learning to speak another language requires social interaction.

You're not getting enough practice and/or exposure.

There are so many different ways to learn languages. I think the way they teach in schools is sorta autistic and un-natural. Sure it's important to learn all the rules and grammar but there is rarely enough oral practice.

I suggest you forget about the tiny details and just find someone who is a native speaker in whatever you want to learn. It's important to have confidence even when you don't know what you are doing and learn from mistakes.

Because you're not immersed  OP.

Kids know the basics at 5 because they've been around the language (their parents) for five years.  Of course it's different with kids but if you were bombarded by the language you want to learn constantly then you'd start learning too. 

How are you going about learning anyways?