The HN audience values hack values[0]. Often things are done for the sake of novelty. Show HNs that reach the front page often demonstrate hack values or novelty or utility to the audience. You know, the "it's cool!" or "that's a great hack" feeling when you see it.
I've actually seen your app (and your submissions). It feels a bit run-of the mill. It's honestly just...is. There is no further narrative (well, you did mention that you had no decent option so you built your own). There is no further elaboration of the hacker spirit that many on HN seem to cherish.
Hack values can be signaled in the title of your submission. Your titles seem a bit weak, tbh. I can't tell what clever hacks were made (with the one exception where you said you didn't have better options)
If you don't want to signal hack values, signal utility to the HN audience, and people will respond. Of course the proportion of HN audience that uses WP8 as a platform is probably very small. Out of that small group, the utility brought about by your Show HN is not necessarily shared by everyone. It's probably shared by only a tiny proportion of that small group. Combined with the European time zone that you're in, your chances of reaching the front page is quite small
just my 2cents
Footnotes:
[0] Ouch. My head hurts parsing that sentence