By using a little bit of everything, India's military will never know which bits are in working order on any given day, thus India's enemies will never know what to prepare for!
Things generally work, as maintenance resources(people) are not a problem. Helps having a large pool to choose from. Since the Russian kit is the biggest headache, local industry has been created to support Russian jets. A painful lesson from the 91 fall of Soviet union. The western kit have good support from the manufacturer.