I don't know where you find candidates that can even approach this level of skill or desire to solve puzzles. Most people I interview struggle with a few lines C program coding.
The market for programmers is really inefficient for pay. Google has exploited that to the max and succeeded hiring a lot of very talented engineers at rates you pay for average tax accountants and attourneys. Just like the way they exploited Free software licensing by expempting themselves from the publish part by distributing access to the software not the software itself. That's their two best tricks right there.
Where they crossed the line massively is when they engaged in a criminal conspiracy with Apple et al to act in a cartel keep those wages down. This in addition to all the other legal ways they try pushing the market down when it really should be a sellers market. Andrew Moreton paid less than a football player of similar standing? How about 2 orders of magnitude less.
If you describe a really hard programming job, people self select out. If you describe an easy one, everyone applies.
iOS developer? Floodgate.
Crypto expert? Trickle.
You're comparing a fun job to a job where at best nobody ever says anything to you and at worst, you're taking the blame for the whole company's servers being down.
Most programmers don't need to know how to do this. As it says in the blog he is applying for a security position.
It all comes down to how well you can translate assembly code.
Or send me an email. We're an expensive group to hire though. :-)
Something like : "As much as I am good in making programs I am not good at all in reverse engineering them."
Another dynamic at play is the fact that those who don't have useful skills apply more often as they continue to be out of work, that doubtless accounts for some of it.
Still a bit strange.
Or they've never touched either C or an embedded system in their life, but somehow it ends up on their CV and they tell you about how passionate for learning they are. Which may well be true, but it raises questions about your honesty and/or capacity for introspection. Also, bare-metal embedded really isn't the place to learn C[1], given that most failure modes are "It doesn't work. And maybe something caught just fire."
[1] Ask me how I know...
You could try either relaxing the degree requirements, or reaching a wider audience -- I generally don't see firmware jobs advertised on HN and StackOverflow and those are basically the only two places I ever pay attention to job ads. Depending on your existing volume of applicants you might also ask them to attach a semi-trivial C assignment to their application. Yes, this is accessible to anyone who can google, but you might weed out the disengaged who don't care enough to read the instructions that way.
"Oh I have to stream data into my processing routines with not nearly enough bandwidth? No problem."
I've also had smiles of delight when devs got 100% raw access to every little bit of hardware. Discovering DMA controllers is /fun/ for them. We came super close to getting a decompression routine running completely by our DMA controller!
So, it seems you need to either accept a recent CS grad who seems adept at programming and can learn, or pony up the 200k+/yr to poach someone if you want to hire quickly. Most people I know that have done embedded work tend not to move around a bunch and aren't motivated by small amounts of money to move jobs, so you'd have to offer a large incentive to find the good people.