Granny23, I think in part that is a tone issue, and I hasten to say, not confined to these forums!
It seems to crop up a lot, in my experience, on forums about family troubles in particular.
And it's not even the advice, it's how it's being presented.
"You should just do X" can indeed easily come off the way you describe, when if the exact same advice was presented as "Did you already try X, and what happened when you did?" or "Is there a reason that X wouldn't work for you?" the unfortunate implication you describe wouldn't arise.
It does lead to some unnecessary aggravation on threads with an upset OP and other posters giving advice with good intentions, who now are angry at the OP's upset and irritated response.
It's easy to forget that the OP's problem is very real.