Re: Why is this?
I was temporarily on that RT3 regimen last year myself. It did nothing for me except make me feel worse so I eventually stopped taking the cytomel. In my own personal opinion, I think that the RT3 regimen is not truly very useful. It seems like it is easier to make your RT3 go down by focusing on why it's elevated in the first place. Some things that can cause high RT3 are:
too much or too little cortisol
chronic illness (undiagnosed)
It basically can go up due to any major stress on the body, and once that stressor is eliminated, it will go back down on it's own usually.
IMHO, it would be better to try to find the reason for why it's high in the first place and go from there. Again, this is just my own personal opinion. IANAD of course, just thought I'd offer my own take.
I hope that your health will improve soon. Take care.