Gonna go against the grain here…
I inherited a horse with a pitiful tail. Seriously, laughable. It was down to just his hocks, thin and scraggly, and that was with “benign neglect.” Within the first year, it was down to his fetlocks (at which point I trim it to keep it from getting stepped on), and starting to thicken. It’s now presentable. He doesn’t have a very thick tail naturally (not a ton of hair on his tailbone, and a thin mane, too), so it’s about as good as it can get.
My plan with tails is to keep them tangle-free. If you leave it down and don’t touch it, you’re going to get stuff tangled and that’s what the hair gets broken or pulled out. So I use detangler once every week or two, whenever it starts to get tangled up, and BRUSH from bottom to top, usually in 2-4" sections (bottom 4" of tail brushed out, move my hand up a few inches, brush it out, repeat).
I don’t believe in tail bags, because you’re basically creating the tangles that cause breakage. I think it takes may more work to keep a tail healthy and full in a bag versus loose. But that’s just my experience, maybe other folks don’t mind rebraiding that often.