Main reasons are Cost and Mileage. With all features which I got in Celerio, if I had gone for Grand, it would have costed me 1 Lac more. Besides Celerio claims mileage of 20 Km/L in City, while Grand claims 16 Km/L.
If I decide to travel by Car daily to my office, it would be economical to use Celerio and I have to travel 50 Km daily. Even if I change my job, I would need to travel minimum 30 Km everyday considering other locations in my city. So I needed economical car. And my budget was actually 5 Lacs only, but after insistence of Salesman I gone for ZXI which was bit costlier.