Probably because the blog post is an advertisement for their product, which already allows you to implement bastion hosts as you describe.
From the bottom:
> Databases do not need to be exposed on the public Internet and can safely operate in air-gapped environments using Teleport’s built-in reverse tunnel subsystem.
Not sure what there reverse tunnel product is, but a bastion host is super easy to implement, just spin up an ec2 and walla.
Curious as to what value they are providing
https://www.collinsdictionary.com/dictionary/french-english/...
Haven't used them myself but I wouldn't be against trying it if in the market for something like that.
The same is true for server applications that have weird 3rd party dependencies that may go down when you least suspect it.