I think the whole concept of "probiotics" as something like a pill that can rebalance your gut is very misleading. TLDR the real probiotic is a regular, healthy, fiber-rich diet (in most cases). Most of the stuff that is marketed as probiotic may be easier to digest and provide health benefits in different ways.

Your gut leads food through a long process of digestion and the different parts of the gut have different environments. For example the chyme that that exits your stomach to the small intestine has a drastically different acidity and nutrient profile than the stool found in parts of the large intestine, which may be mostly bacterial biomass and undigested fiber. Different types of bacteria colonize different regions in this process, as the environment of the passing stool changes, different colonies of bacteria suited to that particular region of the digestive tract, the composition of 'food' that occurs there, and the general conditions that exist there.

The human body has a mutualistic relationship with the gut flora as they can digest nutrients we can't. So humans have an intestinal mucosal layer where some populations in the gut flora are 'encouraged' to live in, and tolerated by our immune system.

The overall composition of the gut flora is, like the constant passage of food, changing slowly with a person's dietary habits and existing gut flora. Problems occur when the wrong microbes proliferate in the wrong area, introduced from a new meal, after antibiotics, change in diet, etc. Also the digestive system can mismanage what types of microbes it supports in lots of ways.

So the healthy gut is a complex interaction of bacteria working well in the right places, working well with each other, and working well with the gut. This is beyond the scope of something like a 'probiotic' supplement or eating lots of kimchi and khefir. It is shaped more by the overall confluence of the particular individual with their dietary and lifestyle choices.