RHEL is an enterprise OS. It is designed to handle various drivers (video, network, storage). It has monitoring, auditing, reporting stuff. Some of those dependencies are bringing others (say the monitor needs a mail client to sent messages, ok, install the mail client, oh looks like that brings in perl, etc). Then there might be multiple version of said monitoring. And think they just never really try to make it small. That is just what their customers pay for.
If Alpine did what RHEL does out of the box it would be hundreds of MBs as well.
Atomic is intended to be used as a host OS and uses RHEL, CentOS, or Fedora as a base typically. And the installer ISO is that large precisely because it bundles hardware, language, and all kinds of other support.
However, if you'd like to craft your own minimal Atomic host, you can.
Making minimal containers is pretty easy, though, since yum/dnf lets you create execution trees that contain only what's needed for an application to run (as others have mentioned).
So, really, doing micro-services on RHEL/CentOS/Fedora hosts is pretty easy.
If Alpine did what RHEL does out of the box it would be hundreds of MBs as well.