Why do debit cards do not have details embossed in it like that of credit cards?

because a debit card transaction is via online transaction only, whilst a credit card transaction can support the traditional way of using the zip-zap machine. This is proven useful when you use the credit card in foreign countries where their ICT infrastructure is unstable or none at all.

By this virtue, we can conclude that credit card supports online / offline transactions and debit card only supports online transactions.