I think this is why this doesn't shock (shock!) me.
We're talking about a curated, supported, official image here, right?
If folks want to use a "MyUbuntuImage" they or someone else packaged and uploaded, more power to them.
But by pulling a Canonical image, you have a relationship with Canonical. Expecting that relationship not to exist "because open source" seems to be misunderstanding who does what work.
As to whether this should be opt-in, done, etc. is another matter entirely. But the fact that it exists at all doesn't feel particular shocking.
It's not like we're talking about everyone who pulls a RedHat image's info being sent to Canonical!