Help me ask why you didn't just

I would just say "why can't you just use xxx". If they are moderately competent, they will instantly say "xxx doesn't work for this because the abc can't be compiled on this hardware", they'll have thought of it too, because it's probably not just obvious for you, and now they have helped you get up to speed on this complex problem.

I don't think you can use magic phrases, or avoid magic phrases, to manipulate people into feeling one way or another about you. You aren't insulting them by asking obvious questions, you need to hear the answer. If it took them 2 weeks to get stuck and ask for help, it's going to take you at least a few days to figure out why this is actually a harder problem than it seems. Avoiding the 'obvious question' because you think your colleague is too fragile to answer it and think nothing more of it is far more condescending.

What if they didn't think of it? Either they are very inexperienced, so they shouldn't be insulted by an expert providing expertise, or they are experienced and will slap themselves on the head and laugh about it, or they are an intolerable jerk, and who cares what jerks think of you?

"Why can't you just" is a huge pet peeve of mine.

"Why can't you just" is particular frustrating when someone interrupts a deep conversation. What they're really saying is "can you please stop your conversation and focus your full attaching on catching me up to all the issues you discussed 2 hours ago?"

Here's an alternative:

"Can you tell me about your problem?" Then shut up and listen.

And here's a slightly longer form:

"You've thought about this way more than me. I'd love to brainstorm with you. But I'll need to catch up. So why doesn't sshd work? Ok, and why can't you foo? Oh damn. What happens if you bar? Dang. I don't have an answer yet, but I am starting to understand your problem".

Odds are decent that someone will solve their own hard problem by using you as a rubber duck. Odds are very, very low that you'll solve someone else's hard problem by offering up the very first thing that comes to mind.

“Why” is inherently accusatory and should be avoided. The question seems insulting because of “why” and “just”.

Try saying “what is preventing us from us Hong sshd?”. It is less accusatory and more inclusive.

"Could sshd have solved this?"

The phrasings listed seem to bring in the other person's choice and thereby create an oppositional/contrastive/comparative dynamic in to the statements.

I write this having struggled with this sort of thing.

It's hard to ask this way without coming off the way a teacher comes off to a student. If you're in a mentoring situation, this clearly works, but if you are a peer or a superior, it's dicey without perfect tone and body language.