Some languages are more infected than English (English). What is the answer to your question “Why”? This is simply how the English language developed. You can trace similarities between English and Germanic languages, and you can look at the history of the language as influenced by political and social factors over time. How do the Normans speak English fluently? How did they communicate so quickly when the English language had become plain?

Do pronouns have inflected forms? “It” is so many things when there is no subject but an object in it. In practice, this means it is as much as a subject.

What extra information is communicated by expressing object / subject?

I can’t think of a case right now where you would use the extra information outside of poetry. The she I despise. He that I despise.

What is the biggest obstacle that people face with their lives?