Two Reasons:
Deep sand in-filled turf is a health hazard — The sand normally used in deep sand in-filled turf is silica sand, a known carcinogen. The typical backyard putting green will require several hundred pounds of silica sand. It just doesn't make much sense to put that much (or any!) cancer-causing material in your backyard. . .
Deep sand in-filled turf requires more maintenance — Sand blows and gets tracked into your patio area, pool and house. Your putting green must also be regularly brushed and rolled to repack and level the sand. Over time, you'll find you're putting on more sand than fiber.
Mirage non deep sand in-filled turf does not use sand to stand the fibers up. We do, however, use sand (NOT silica sand) to weight down the turf, but only a fraction of the amount used by deep sand in-filled turf. And we repeat, we do not use silica sand.