The idea is that this construction method is much cheaper than brick, at least in terms of material costs.
The most expensive part of building a house is certainly not the bricks for the wall. I doubt that filling and aligning sandbags is cheaper/faster than building brick walls. Additionally, there are extra costs for openings, problems with electrical installation, water installation, wall connections to ceilings and elements, seals, structural engineering, etc...
This is certainly sensible in areas with poor building material supply, low comfort (e.g. unplastered walls, few installations, no requirements for airtightness/insulation, small single-story house) and many cheap construction helpers. However, whether you can succeed with labor-intensive processes in a high-wage country is questionable?