I'm
swamp
I'm the one that they all blame when they've too much to do,
it's very hard to clear of land mines
I'm the one who pulls them in and holds them 'til they're through!
you can get stuck in it
For one that likes to breathe I am a nasty place to be,
heavy and noxious air
Why would you sow, no crops will grow, have you not heard of me?
there's a lot of water and mud and crops can't grow
A land so bleak, oft filled with mists so thick it's hard to see,
because of the moisture it's a very foggy place
Set sail upon and sink in too, there is no help for thee.
it's really hard to walk in it and it's very easy to sink.
OP Explanations
I'm the one that they all blame when they've too much to do,
"I'm swamped!" or "Swamped under"
I'm the one who pulls them in and holds them 'til they're through!
People are weary of swamps for fear of becoming stuck or lost
For one that likes to breathe I am a nasty place to be,
noxious, stagnant, odours and the ever present risk of becoming lost or stuck and drowning.
Why would you sow, no crops will grow, have you not heard of me?
Swamps are not the most useful farm land and have in many places been drained re-formed into land of use to farmers.
A land so bleak, oft filled with mists so thick it's hard to see,
Bogs, marches and swamps in Europe in particular were notorious for a thick, almost ever-present layer of fog.
Set sail upon and sink in too, there is no help for thee.
A swamp isn't the safest place for a boat ride. So much so that to deliberately sink a boat is sometimes referred to as "swamping" it.
A partial definition from dictionary.com
noun
1. a tract of wet, spongy land, often having a growth of certain types of trees and other vegetation, but unfit for cultivation.
verb (used with object)
2. to flood or drench with water or the like.
3. Nautical. to sink or fill (a boat) with water.
4. to plunge or cause to sink in or as if in a swamp.
5. to overwhelm, especially to overwhelm with an excess of something: He swamped us with work.
6. to render helpless.