Looks like everyone avoided the original question. Why are snowflakes
created when they should just form a pellet?

You must have missed some messages.

Two people directed you to http://www.its.caltech.edu/~atomic/snowcrystals/
and Mike Tullett wrote the following:

quote

A snow flake is an aggregation of tens or hundreds of separate tiny ice
crystals. The latter grow within the colder parts of clouds and take on a
crystal structure, well illustrated on many web pages.

The growth is directly from water vapour gas to an ice crystal, with no
liquid water normally involved. As the falling crystals bump into each
other, they often join (at fairly high temperatures) to form what we see as
a snow flake, containing much air, both in and between the crystals. If
the lower air is sufficiently cold, these flakes can get all the way down
to the ground, but usually they melt to produce what we see as rain.

So your idea of "water expanding to form a flake" needs to be re-thought:-)

/quote

So either your news server is misbehaving, or you're reading your messages
too late at night :-)

Anne