The gut microbiome necessary???

Looking for an educated answer for a question, please no highly speculative wishful thinking.

If the Microbiota is so important to our immunity, mental health/mood, nutrient absorption, metabolism etc. and the vast majority (an understatement) of the microflora reside in the large intestine, why is it that people who have had their large intestine completely removed are able to live nearly normal lives enjoying many foods, not needing to live in germ free bubbles? Also note that they don't suddenly develope mental disabilities or other disease states attributed to poor gut flora??

I ask this because I have a personal interest in the topic as my health is at risk.

Thank you in advance to all. Tweet