They could have always supported software for that long. They simply refused to.
There is no benefit to slowing the release cycle. All of the research gets done either way, all of the supply chain modifications get made either way, and as an individual you have no need to replace your phone every year. A multi-year release cycle does very little but screw over people who need a new phone during the wrong point in the release cycle, while also substantially complicating the supply chains by making demand much spikier.