Why did China and India order several aircraft and helicopters, respectively, from the US and not Russia?

China/Chinese airlines recently ordered 300 aircraft from Boeing [including both narrowbody and widebody planes], while India ordered several Boeing military helicopters. At this point one is forced to wonder - why did China order 300 passenger planes from the US - it's biggest adversary - and not from Russia, especially when the latter needs all the help it can get at this point? In the case of India, the decision to get even closer to the US is more understandable - shrewd Boeing officials most likely paid bribes to the guys responsible for making the decision, and the Americans thus won the lucrative Indian order.

But what about China? Why didn't China instead order Russia's 21st century airliner, the Irkut MS-21 [MC-21]? If immediate deliveries are a concern, then with such a large order, China could've ordered a mix of Boeing and Russian planes, especially when the MS-21 is expected to be a comfortable, efficient, modern and safe airliner on a par with contemporary Western narrowbody planes. This is hard to understand. China could've single-handedly propped up Russia's legendary but needy civil aviation industry and would've surely secured a two-way win-win deal for both the countries in the process.

I'm pretty confident that if Boeing's Completion Center was a strong attraction for China, Russia's UAC would've also been happy to setup a similar center in China for the MS-21, if it had been promised a 100+ or 150+ order for the plane from Chinese airlines and also the flexibility to export.

Why didn't China help Russia in this time of need?

[UPDATE]: Even more curiously, why does Iran have plans to buy several Airbus/Boeing planes? Why doesn't Iran buy planes from its friend/savior Russia instead [Superjet 100, MC-21, Il-96, etc.]?

[UPDATE]: I just realized that I have little right to complain and protest about China/India/Iran not purchasing Russian passenger aircraft, when top Russian airlines [example, another example, and another] themselves prefer and operate Airbus and Boeing planes. Sigh!

[UPDATE]: China just placed a massive order with Airbus and with Airbus Helicopters. Sigh.

[UPDATE]: And indeed, Iran confirmed plans to buy 114 Airbus aircraft soon. Nothing Russian. Sigh. What's more, this WSJ article says that "Iran keen to re-establish ties with Boeing".

[UPDATE]: And Iran "invites" Boeing for "talks". Sigh.

Update [21-May-19]: The China-US trade war is in full swing currently, and US is punching China with its full might, yet China still won't use its buying power / market power to severely hurt Boeing and give a much-needed boost to the only credible challenger to the Western duopoly - the Irkut MC-21. Sigh!

Update [1.10.21]: These days there's much ongoing talk about the US choking China's C919 program by blocking / delaying American components. What I don't understand is, why wasn't this scenario anticipated earlier by the Chinese? After the ZTE saga, it should've been obvious. Even more so after the strangulation of Huawei. And it isn't like there aren't alternatives - Japan, South Korea, Turkey, Germany, Italy, Spain, France, Russia, China itself, etc. The de-risking of C919's components should've been done right from day 1. Hopefully the CR929 will be protected from these issues.