The specific reason for catering being in demand would vary depending on where you are living. However, the general reasons for an increase in the demand for catering are somewhat similar in all places.
First, the demand for catering is likely to go up as people become wealthier. As they do, they are able to afford more in the way of luxuries. Catering is surely a luxury and therefore increased consumer income would lead to increased demand for it.
Second, if people's lives are becoming busier, catering might be more necessary to their lives. If they are too busy working, then they might not be able to do as much cooking for themselves. This may be especially true as women enter the workforce.
So two major factors that would increase the demand for catering would be higher incomes (so more people can afford it) and busier lives (so that more people need it).