Explaining alternative travel routes when going to the USA [closed]

Just be honest.

Whatever you do, don't lie. Don't make up a "more reasonable" story, don't say that the ticket was cheaper if it clearly wasn't, etc. If you're doing it just for fun, just say so. It may catch their attention and you will likely have to answer a few related questions, but as long as the story is true, its your best bet. Taking a detour for fun is probably not correlated with being an overstay risk; lying about anything is (and can easily get you banned for life).

Border officers (and airline staff trying to estimate what the border guard will think) try hard to uncover the slightest inconsistencies in your story, so that they can catch you lying. The safest way to avoid being caught lying is not to lie at all.

I would like to expand on the hard rule "do not lie at an airport" and add a companion rule "never furnish information unasked". Both for security and immigration always answer politely, factually, to the point but never drag out, pad, whatever you call it.

Also, never make up these elaborate fantasies on what security / border guard might think. You most certainly lack the training to even come close. Spending a transoceanic flight making up stories to present at immigration at the landing point is a recipe for disaster. If you think "your case is special" it almost certainly isn't. (This site is a good resource for both side of the coin: both showing how many cases are not special and then what it takes for you to be special, for example this I don't know my nationality. How can I visit Denmark? insanity)

I feel that, when questioned, they won't be satisfied if I'm telling them I'm doing this for entertainment

See, this is the fantasy you are spinning. There are no reasons they wouldn't be satisfied, there are blogs, vlogs and more literally titled 'flying is fun'. And even if they are not, the totality of your circumstances will decide what happens. Lying to agents trained to catch lies, however, that never leads to anything good.

Is there anything I need to be aware of with this approach?

Not really. This was probably just a routine control and you got unlucky. Most likely this was a doc check executed by the airline, as the Schengen exit (if you needed one) really wouldn't care. However, the US heavily fines any airline that brings a passenger who gets denied entry, so they are motivated to be extra thorough when checking US entry requirements.

Taking stopover flights is perfectly normal and very common. In most cases it's substantially cheaper than non-stop flights. For example AMS->BOS is much more expensive than DUS->AMS->BOS, because of "revenue optimization" airline pricing. An answer like "this was the best fit for my schedule and budget" should be more than enough.