I don't think it was purely Facebook that killed MySpace and AIM, it's that they didn't get on phones quickly enough.
However unlike SMS it didn't cost eye-watering amounts of money to use. Whatsapp never became popular in the USA because most people on pay-monthly contracts received large SMS allowances.
In the rest of the world, networks felt threatened by SMS -- if texts were too cheap then people would stop making phone calls! So it was universally crippled with ridiculous limits and fees. Even in 2018 it costs me a lot of money to send an SMS, and I don't know anybody under the age of 35 who uses it.
AIM and AOL were popular when we didn’t have texts or even cellphones. It wasn’t so common to give kids cellphones early in those days.
As another person pointed out, I can send the message to the people I want not followers.
Within a few months of push notifications first being available, WhatsApp was released for iOS, in November 2009.
[1] https://www.macworld.com/article/1135141/aim_review.html