From https://www.paypal-apac.com/india/
In order to comply with the RBI Guidelines, our user agreement in India will be amended for the following services as follows:
1.Any balance in and all future payments into your PayPal account may not be used to buy goods or services and must be transferred to your bank account in India within 7 days from the receipt of confirmation from the buyer in respect of the goods or services; and
2.Export-related payments for goods and services into your PayPal account may not exceed US$500 per transaction.
Many online publishers / webmasters earn more than $500 from advertising from a single source, so the ad network will either split the payments or use alternate payment methods. As conditions change, you always find new methods.