Question

why alauddin khalji used to pay his soldiers in cash rather than iqtas

Answer 1

Alauddin Khalji raised a rather large army of soldiers, all of whom had to be paid. Thus, Alauddin chose to pay his soldiers salaries in cash rather than iqtas as the soldiers would use that cash to buy their supplies from merchants in Delhi. It would also have been highly improbable to give iqtas to tens of thousands of soldiers.

However, he did pay his generals in Iqtas.