There is a significant difference between spoken and written discourse.
When speaking, we have a multitude of phonological features to help communicate our ideas. These could range from emphatic stress, stress timing, intonation, chunking and others. Because of this, we don't necessarily speak in sentences. There are far more interjections, discourse markers (you know...) or ellipsis (cutting out words: She was trying to obviously give...). This is especially true when speaking in stream of consciousness as is this deposition of Ms. Lewinsky.
When writing, as we have more time to structure a thought, there is greater emphasis on punctuation and cohesive features. United States Public Law 111-274: Plain Writing Act of 2010, found that 20-word sentences were a reasonable benchmark for maintaining ease of reading. Of course, obviously there are countless exceptions, particularly in more creative writing.