It’s all fascinating - I cannot even remotely keep all the interrelated processes straight, but it seems like there are frequent new additions to the “high-carb and poor blood sugar control can do this (bad thing) to you…”
Some of the sentiment to the contrary comes from misunderstandings, like “Keto means you eat more protein than is good for you,” etc. Hey - unless one’s kidneys are already in really bad shape, even a “really huge protein” day ain’t gonna be no big thing.
Part of it is just losing water - usually, each carbohydrate molecule has 3 water molecules hooked on, and with very few carbs we’re not having the attendant water any longer. As we quit digesting much in the way of carbs, we go to a ‘less water-retained’ state, that initial fast weight loss most of us experience when going to ketogenic eating.
With less water in our bodies, we excrete some salt and other electrolytes, to maintain the concentration of them in our blood and in and between our cells. This, by itself, is really not “flushing electrolytes” - if we didn’t, we’d have too much of them in us. High carb makes us have more total electrolytes in us than keto, really just since we have more water in us. It’s not bad to lose some when we don’t eat many carbs; it’s the body maintaining the levels it needs to.
I also think there’s a tendency for people to over-emphasize “getting enough salt,” etc. If there’s a demonstrable shortage or if one feels bad and then adds some salt and feels better - then no argument. Yet there are also people who fast for 30 or 40 days with just water, no added salt or other electrolytes.
The body is not going to be excreting many electrolytes at such a time, maintaining the balance it needs. Evolutionarily, we didn’t have salt shakers, so we got some salt from the blood and meat in some of our food - think of those big old animals we hunted, most of them eating grass and other veggies all the time - they were getting some sodium here and there.
While eating low-carb may mean needing more salt, etc., especially early on after giving up most carbs, I don’t think it necessarily needs to be “feared” on that score.