"I did it as a lark" has been used as an expression for a long time already, well over a century.

To give a few examples, https://www.google.com/books/edition/The_Boy_s_Own_Annual/X7...

"Sure as goodness, I thought you both did it as a lark", from a book published in 1895, so it's reasonable to assume it was already in some level of common idiom by then. It's unlikely The Boys Own Annual was trail blazing in its use of language.

Or https://www.google.com/books/edition/The_Fortnightly_Review/... from 1929. "D you remember I got certified as a lunatic for trying to make a living by betting that one horse would reach a post before another, I admit it was silly, but I only did it as a lark"

Language changes and evolves over time. You're attempting to be King Canute, except maybe one apparently deluded enough to believe the courtiers, only not as the tide is on the way in, but as the tide is long past and you've almost drowned.

The ship sailed on the point you're making before you were even born.