You answered my first question.
You didn't answer: Do you trim? If so, how often?
You didn't answer: Do you seal your ends?
So if I'm to guess, your answer is no. So you have shoulder-length hair that is manipulated into styles daily. In a ponytail, your ends are left exposed to the drying air. I tried to see what your wet bun looks like coz lawd knows my hair cannot form a bun when wet and it's a little longer than yours, but I couldn't find one in your album. Do you have a pic of your bun?
So what's happening is your retention is bad. Friction from styling tools/manipulation wrecks havoc on ends. So does their just being in existence over time. And if you're not sealing, you leave them even more vulnerable to the effects I just mentioned. Add to that the absence of trimming and you have a sad story of no progress whatsoever as the ends just fall away on their own, taking with them a portion of hair that might've been saved if you'd made a nice clean blunt cut. You see ends don't break off like a twig if left to their own devices. Instead they tear off, a split extending up the strand into areas that were nice and whole till it tears off, thus affecting a section of the hair that didn't need to be damaged. And before you know it, what's left is a "mist" of hair that blows away unnoticed leaving you right where you were.
I will let you process that for now, and then if you are interested, I'll be happy to share my own journey in pics so you can see how the things I mention above really do affect retention. And if it's any consolation, my retention is not very different from yours--which is 1/4 of what it is supposed to be--for the same reason I mention above.