There's a lot of speculation about what happened to Altoids Sours, but the simple answer is that they didn't do well enough in stores to keep them in stock.
Altoid Sours were originally launched in 2004 as a spin-off of Altoids Mints, and they were known for their distinctly tangy exterior and fruity punch afterwards. By 2010, sales began to slow and a Mars representative said "They were discontinued due to low national demand."
In the years following its removal from stores, there have been many social media campaigns and petitions to bring the candy back, with no avail.
That's why we at Sour Drops have decided to bring the memory of Altoids Sours back! Currently, we have Tangerine, Mango, and Green Apple with more on the way.