The difference? The first one was harder, and its explanation was a block of text. The second one was (relatively) trivial, and it had a short explanation.
The harder one got no answers and 12 upvotes in 112 views, and was up for more than twice as long.
The easier one got 19 answers and 9 upvotes in 141 views.
It also just so happens that the easier challenge is currently in HNQ. Now, I believe that the easier challenge does have a place in PPCG and even in HNQ. However, I believe my harder challenge is much more interesting. I've posted similar harder or easier challenges in the past. My highest voted challenge was exceedingly trivial, and was on HNQ for quite some time. Another harder challenge did fairly well, probably because I put a significant bounty on it - but it never hit HNQ.
I think there's a problem here, although I might not speak for the majority. I don't know if there's a solution, but we may as well have discussion about it. I'd like a way for harder challenges to receive some attention.