There's loads of interiority, it's just very codified. Once you know the code, it's easy to spot, though it's not immediately obvious to modern English speakers. Sadly, like Shakespeare, Austen is often taught Very Seriously, so all the naughty little jokes and personal giveaways are missed by poor students looking for the Great Literature.

I once had a student arrive at university convinced there was no sex in Shakespeare, and when I said 'country matters?' in a joking fashion, looked at me blankly. I sighed.

In the seventeenth century there was a man named Nahum Tate who went around revising Shakespeare to cut out all the 'uncouth' bits. I fear many teachers still do the same.