What I can't understand is
why this coin suddenly lost all of its momentum??

I mined it from day 1 until POW was essentially done and it seems like everyone lost interest.
Its not that peeps lost interest, they lost faith in the developer because of his/her/their lack of activity. Soooo many scam coins about, lots of peeps getting scammed and loosing their investment money.
You can understand why peeps are quick to call scam if they suspect something odd about the coin or the dev. Even the slightest hint of a scam can severly effect a coins market value.