Personal opinion so please don't kill me. I have no intention of offending anyone. Just opinion. So, I'll apologize if this offends anyone.
I don't think he is not noticed, or not many people notice him. Judging from the views of his videos, he is quite noticed. Maybe not in the overseas (non-Japanese) community, but from his twitter and stuff, he looks like he is noticed well by . Plus, he already has a page here. Overseas fans can easily accidentally stumble upon his page and becomes a fan. I know someone who accidentally stumble upon Kanseru's page and became a fan.
If you say someone unnoticed, it's probably Sorao, singing for 4 years but 12,000+ views on her most popular cover,.. she started off pretty bad, but she is getting better, like, a lot better. Just looking at the number of views in her videos hurts me pretty bad.
What I want to say is, If Megater is not noticed by many people, then Sorao is probably not noticed at all. The way overseas notice utaite, are probably here, utaiteDB, or YT. It's rarely from their own searching in NND as most overseas don't understand Japanese well. Even if there is google.translate, or NND in English version, it's still not 100% useful yet.
But, I really like you trying to promote (? is promote the word?) him. So personally, instead of asking why not many people notice him, I think it's better to say 'Please notice him more' (or not sure how to phrase it) :)