Why is installing ORACLE ODBC client a complex task?
You've pointed to instructions for installing the Oracle Instant Client.  That is a very slimmed down version of the Oracle Client that is intended to be bundled with third party applications and installed as part of their installer packages.  It's not something that normal people are expected to manually install (other than the third-party application developer that is working on building the installer that includes the Instant Client).

If you download the full Oracle client, you'll get a nice, friendly GUI where you hit Next a bunch of times.  The issue is that it's much bigger (because it contains a lot more options) and it's more difficult to transparently embed in a third-party's installer.