>>"Probiotics DON'T IMPLANT THE HUMAN GUT PERMANENTELY."<<
perhaps they do... perhaps they change form and or function to do so. So when "science" searches for the ingested "species" it is no longer there having morphed into a form more compatible with the host's terrain.
Many, many things can cause mucosal damage... things as seemingly benign (insidious) as water chlorination/fluoridation, food additives and the pesticides, herbicides, rodenticides, avicides, fungicides, and fertilizers sprayed on our foods... if the mucosa and other layers of the intestines are damaged... "probiotics" may not colonize (in the ingested form anyway - pleomorphism) until the damage is repaired... colonies require a healthy mucous membrane.
These days, that is a hard thing to do... especially if one is not willing to discontinue caffeine, alcohol, pharmaceuticals, especially Antibiotics and COX2's, etc. on top of the insults to the mucosa from common drink and food.
Studies I have found interesting show that when one is taking Lactobacillus acidophilus, bifidus increases dramatically in the feces too... why is this when they are not taking bifidus? Why is this if bifidus did not establish colonies? It is likely because they were there all along and not expressing as "bifidus" due to fungal/yeast overgrowths... the acidophillus creating a more favorable terrain awakens the bifidus strains from their inactive forms perhaps.
Microorganisms are the most adaptive species on the planet...
Read Bechamp and the dozens of others after him on pleomorphism... microorganisms also have the ability to go dormant if necessary... change form, expression and their cell wall make up in order to deal with extremes in environments.
While the "solid" Science may not be there to support colonization... the circumstantial evidence is... and given how much we have physically changed in these modern times, that may be all we have to go on until such time as we eliminate all global and body pollution... not likely in my lifetime.
One other thing... people ate microorganisms daily, and in rather large amounts throughout the ages before food sterilization and refrigeration practices were began little more than 80 years or so ago... so a daily "probiotic" and/or fermented foods eaten daily for life is not a far fetched idea... or need IMO.
I am not disagreeing with you... just giving you some food for thought.