Why apt package chromium-browser installs snap package instead?

For Ubuntu 19.10 it was a developer's decision. See cite from release notes:

Ubuntu 19.10 New Features

The Chromium browser is only available as a snap in 19.10. This blog post has more details.

It is normal and expected.

I had the same problem. I disabled/removed snap/snapd from my Ubuntu and didn't want to install it again because of Chromium. Since Ubuntu and Debian are usually compatible, I installed Chromium from the Debian repositories: https://askubuntu.com/a/1206153/1038363

I've had the same problem. Wanted Chromium, but no via Snap. Found Chromium Dev PPA, works stable so far: https://launchpad.net/~saiarcot895/+archive/ubuntu/chromium-dev