Because most of their weapons are NATO standard.
One reason yes. The major reason is sheer ineptitude of Indian defense planners.
Look at the A330 AWACS plan. No other country has purchased A330 based AWACS including the countries that build A330! This means development will be a long process with certifications delays and plenty of teething problems. Is there an absolute need to do this? No. But Airbus is known to bribe officials all over the world.
When Phalcon was chosen, IL-76 was not even in production! Old unfinished airframes from Kazakhstan were refurbished and completed to mount Raytheon built radome and Israeli radar. IAI had offered G550 and B767 instead but arrogant or corrupt Indian decision makers ignored the offer.
That decision to use IL-76 led to cost overruns and delays of 4 years. But the worse part is that the availability of Phalcon is subpar. This is due to IL-76 maintainability issues. It is a gas guzzler aircraft with high cost to operate.
Meanwhile, Pakistan purchased 4 Erieye for $186 million each plus support, training totaling around $1 billion. They used SAAB 2000 aircraft that are cheap and efficient. On time and within budget. They followed up with newer Erieye recently.
One can discuss multiple such thoughtless efforts of Indian defense officials that have deeply damaged Indian defense industry and preparations despite spending significantly more money than Pakistan. Subpar Mirage upgrade, harried Rafale purchase, leasing old Soviet nuclear submarines for $15 million a month, not making LCA program a priority.... list can go on.
Coming back to AWACS,
India already has EMB-145 based 3 functional AWACS and all that needs to be done is induct more E-145 based platforms with updated engines and power supply. Embraer should pay penalty for bribes in the past.
Yet, now there’s a talk of using C-295 for this work. Again, no other country including the manufacturer (Spain) has used this platform for AWACS! With slow speed and low ceiling, C-295 is probably not a good choice anyway.
There’s a saying: A bird in hand is better than two in bush. Hopefully, someday someone in Indian defense planning will decipher the meaning.
PS: Not going to argue about 360 vs 240 degree scan abilities. That is an issue only for keyboard warriors and corrupt officials who need to justify a purchase. It’s nice to have but not a must have ability.