Subscribing to ESM throws error - "ESM is not available for platform ppc64el"

Tried ESM. And here's what it throws :

# ua enable esm-infra
One moment, checking your subscription first
UA Infra: ESM is not available for platform ppc64el.
Supported platforms are: amd64, i386, i686, x86_64.
#

For now, I did a free subscription to check. Wondering if ppc64le is supported with buy subscription only. However, when I attempt to buy, it doesn't mention anything about ppc64le as well.

I am now fine to even do a reinstall of Ubuntu newer version (say, 18.04) rather than upgrade. However, I dont have access to CDROM drive or a USB. If at all there is a way to install newer version from the command line of the existing Ubuntu OS on my system, please suggest the commands. Whereas, I do read somewhere that that's not possible!

Please let me know how else do I fix this mess?

PS: This question is a follow on to Unable to upgrade Ubuntu 16.04.7 to 18.04. No packages needing update, yet throws "Please install all available updates..."

Based on the Ubuntu Wiki for the ppc64el platform, 16.04 is no longer supported; even under ESM. If you upgrade to 18.04, then you will have a little over a year of security updates remaining:

As for the upgrade process, how did you install 16.04 (or an earlier version) if not by DVD or USB? Can you machine boot from any device other than the internal storage device(s)?