It is not selling as well as Mazda had hoped - there was an article in Automotive News that alluded to Mazda targeting 90,000 CX-90 sales and and additional 30,000 CX-70 sales (article archived here to avoid paywall:
https://archive.is/etYVc). In comparison, Honda sells around 100,000 Pilots in a year, so these were not outrageous targets. However, they were certainly very ambitious (bordering on wildly optimistic) as the CX-9 sold less than 35,000 every year it was on sale.
Given Mazda's assumption that the CX-70 would only move 1/3 the volume of the CX-90, that implies only ~16,000 CX-70s given the CX-90s actual sales numbers. So, you can see why they pulled the plug. Of course, given Mazda marketing's track record, the CX-70 will probably outsell the CX-90.