Here's the deal .. movies released then had the luxury of parallel releases of top stars without interference as they had their own space - theaters that would host them of 150-100-200 days etc. if needed. They could still all end up hits or better. Situation now is very different .. the current day movies releases try to saturate the market space for a shorter time and hope for their break even quicker like in a week/2weeks. They would try to achieve hit/bb status in a month or couple of months. Multiple releases of big stars simultaneously would seriously jeopardize that plan. Eg. releasing Ajith and Vijay movies together will seriously affect both movies ..