It's a bit hard to explain. It comes down to 'politeness'. In English, the more indirect your sentence is, the more 'polite' it is. Commands are given in very simple English. For example:
"Don't eat that." is a very strong command.
"You shouldn't eat that." comes across as being a little judgmental depending on how you say it.
"You shouldn't be eating that." is so indirect that it almost sounds like you're pleading with the person not to eat it. However, it's still direct enough to be considered a suggestion.
"I've heard that's bad for you." is about as indirect as you can be, but this level of indirectness actually annoys some people.
A little-known fact about English is that we do have levels of politeness that are every bit as difficult as some of those East Asian languages we complain about learning. The difference for us is that tone is the most important part of being polite or not. Even so, the linguistic structures do exist.
On here, for example, when people say, "That's wrong." it makes me cringe because it sounds so impolite to me. I would say, "It's not correct to say X." because it's more indirect and, therefore, more polite.