So many of these scripts basically derive from Brahmi which was famously rock-cut (Ashoka monuments). That type of medium is well suited to angles. Major scripts including Tamil were also enscribed on to metal .. this image shows an evolution directly away from angular toward rounded. https://www.instagram.com/p/CpB1ygEPwJt/

Presumably this reflects a shift from courtly scribe closed-door literacy toward more popular literacy specifically including temple-trained monks who presumably could not have afforded either stonemasons or metal plates for general use.