Clearly they were concerned about the off-hand chance that there could be some magic in that old silk hat they planned to put on his head. I mean come on: at more than 16 feet tall, the resulting thumpety-thump-thump could have leveled the entire city. Furthermore, a snowman that large arguably wouldn't even pause a moment if a policeman were to holler "stop".
Weirdly, Snowzilla reappeared anyway. "Magically", per the Anchorage Daily News. In the same article, the owner of the land on which the huge snow man is built seems to be getting the Joe the Plumber treatment from unnamed "officials".