Maybe the context helps explain it better.

But…

Cherry blossoms are very light pink and pretty, and there are very many of them together. possibly represents happiness or joy / being part of a group.

Wind is generally considered to be in the sky; it swirls around but goes ultimately in the same direction. Possibly means progress, an enjoyable forward motion in life, towards life goals.

Drifting seems to represent a lack of control. Just drifting along where ever the tide may take me, type of thing.

The sea, depending on geographical location, is much darker than the sky. More muddled, and certainly further down. It could be considered the lowest level before the depths of the earth. (sea level being zero height, and below sea level being in the depths… the underworld perhaps)

It’s movement is seen as back and forth, without real forward momentum; and in some cases stagnant.

Also being one drifting in the sea compared with many floating on the wind makes the one seem pretty bleak.

Cherry blossoms in the air remain crisp, clean, and pretty;

but in the ocean the become soggy, cover in salt, and slowly sink.

I would say the this author has great expectations for the quality of life that he should like to be living, and feels that his life is very poor compared to those expectations.

The author possibly sees all of society flitting about making life look so easy and joyful; and he/she is stagnant, sad, lonely and barely able to keep head above water.

Hmm.

Kind of a sad image.

Life, in general, is great; it soars like beautiful cherry blossoms at their height of heights.

My life, however, is an abysmal, stagnant, unmotivated drift slowly sinking from the lowest point it could possibly be.

where is the joy in that?