We are hitting the SBD debt limit, then rewards start getting split into liquid steem and steem power, eventually you won't get anySBD in rewards unless someone or many do the conversion of SBD to Steem removing it from ciculation and reducing the debt.

I am not too clued up on it but that is why we get the split rewards though.
https://steemit.com/steem/@themarkymark/sbd-haircut-rule-is-about-to-activate-do-not-convert
https://steemit.com/steem/@tarazkp/dust-to-dust-sbd-to-steem