I honestly don't remember when last i heard that platforms like Facebook, Instagram and even Google suffer from a DDos attack, it's been a very long time I heard of such and I guess that must have been when the company was still growing, even the google outage you are talking about is also something I know nothing and have heard nothing about, except there is the possibility of the platform experiencing an outage in country or continent while it's available in another.
The reasons as to why you don't remember could be because;
1. you rarely use the platforms
2. DDoS attacks could have happened when you were offline, and they had everything in control by the time you started using the platform.
But all in all, no platform is immune to such attacks. They eventually happen one way or the other.