My sage has never flowered before, so this was a pleasant surprise! I’m surprised it’s not commonly grown as a decorative plant now that it’s put up these very pretty purple spikes of blooms!
Sage in the ground is a perennial around us, but it only lives 3 or so years. It usually flowers in year two. If I had to guess why it's not more common as an ornamental plant it's because of its lifespan and no flowers the first year. People gravitate toward annuals and perennials, not biannuals.