Here's just a little insight as to why the maps were removed, and why they probably won't be returning.
Freeze Island was removed because the community, at the time, came to dislike it. There were many people complaining about how long the ice chases went on.
Moonlight lake was removed because it had an unfair spawn, it was too small, and the builds were very poor.
Wyvern's Wake was removed for multiple overpowered items being found, and will not be returning because the map maker has requested it never return.
Boombeard's Battle was a very pretty map, in my own opinion, but was ultimately removed for there being too much water, making it difficult to play.
Solar Frost v1 was removed for there being too many spots you could escape the map, and for being too small as well.