Over about two years, several changes have been made to support SMTs, even before these latest changes that are about to be tested. We got AppBase, which is important for scalability. Without AppBase, adding SMTs would have been a tall order.
We needed Resource Credits before SMTs. We also got Mira. Similar rationale. Scaling after SMTs would not be a good idea.
You could say that AppBase, Resource Credits, Mira were prerequisites for SMTs.
So, to say that SMTs weren't the focus for over a year is inaccurate.