Why is spoken English easier than written English?

Spoken English is easier because we needn't bother much about correct grammar when we are speaking whereas pronunciation and fluency alone matters. Sometimes mistakes often get overlooked in spoken English. In written English everything matters, correct grammatical structures, your vocabulary, your style in writing and so on. That is why written English is much more difficult. 

Spoken English allows you the scope of error, whether grammar,pronounciation, word use or the incidence of  cultural influence on the language.  I find written English to be much easier as it allows me to articulate and involve creativity in my expression to a much greater degree than a conversation. Conversations are often built on recollection and assimilation rather than a genuine expression of one's thoughts and feelings  (please note, i say often and not always).  Written English allows me to express to my heart's content and my head's self esablished standards of delivery. Did i reach this level through a comparison and segregation of learning a language in Spoken and written formats? Certainly not.  I simply learnt a language and tried to express myself in both forms. Writing improved my conversations and vice versa. Consider your question redundant and try to write as much as you can. Soon you will realise its merits and how it improves your spoken english. i can help you out if you wish.

This is absolutely a brilliant question i have seen here, after a long time. It invigorates me, so i will try, very humbly.

No matter how it happened, the handiwork of the Almighty or the evolutionary process, this much is clear that human beings have been bestowed by a reamarkable faculty which othere specise do not possess, and that is speaking.

Listening and Speaking, both are natural phenomenon whereas, writing and reading is an aberratuion, somethimg which was not supposed to happen but, whatever be the argument, it did happen. 

Therefore, Speaking and Listening will come naturally to us and should be easy as compared to the other two.

Taking it furthere, if one wants to improve their speaking and writing skills, the source will come from Listening and Reading. 

L=R>w+S (QED)