Its not much different than sending alerts by email or SMS which are also privately controlled.
See, this is where you're right, but very wrong. You are correct in that text and email are privately controlled, but they arent comparable to Twitter - in scale, composition and ownership.
Email and SMS are open protocols that are not controlled by any one group, and the systems are all interoperable and open standards control how they work. Twitter is a privately controlled platform with no visibility into how it works, no interoperability with other services. The better comparison would be email and SMS to the fediverse.
But, those systems have maintained a reliable amount of freedom where as Twitter has gone off the deep end.
That goes back to openness, standardization, and interoperability of email/SMS. Because of all those items, no one person can disrupt communication because there's no central control.