You can download NepTunes for free but some features requires NepTunes PRO. You can unlock it with a yearly subscription (with a free one month trial) or a one-time purchase.
Great question. The software is never "done". And it takes substantial amount of time to make something like NepTunes to be as reliable and polished. The app has to deal with 4 different web APIs, two different music players and their APIs, bugs in them, tracks with missing metadata etc. It took me over 6 months, working almost every day, to create the 2.0 release and it was missing a lot of features!
Btw, I'm also not a fan of subscriptions… I don't have anything against this model – it's just because most of subscriptions are overpriced. And I don't want to do the same thing that would personally pissed me off. And few bucks yearly for a non essential features is a cheap subscription. I will have stable stream of (small) revenue, and you, as the user, will know that you didn't pay 30 bucks for an app that will be killed 6 months later.