What would you propose they do differently?
That way all of the people who missed the news about Heroku and first heard about it when sites they were using stopped working would have a fighting chance to recover their data before it vanished.
Even better: Salesforce could have actually invested resources in Heroku (instead of effectively feature-freezing it a few years ago) such that the thing where the free tier acts as a major funnel for attracting paying customers continued to work, as it had for most of the lifetime of the service.
if your project used heroku directly without any github integration then they effectively were also your source control.
Just shutting it down and deleting after notifying via email (did notices go to junk? etc?) is kinda shitty to do.