It doesn't show.
Q2. But he didn't want to declare the donation did he?
If he didn't want to declare it, why did he declare it of his own volition but late? If you want to hide it you wait until someone writes to the standards office to complain that you are failing to declare (a la Boris).
Q3. Because he got caught out.
But he didn't. He declared it, just late.
Q4. We don't know, unless he thought he could get away with it, which he hasn't. Tax avoidance, didn't want the world to know some connections he may have, it is part of a bigger slush fund who knows? What we do know though is that he didn't declare it, he has told us that much.
Nope, he didn't. He declared it late. That isn't the same as not declaring it.
Returning your library books late means you get a fine for being late, and you try not to repeat the mistake.
Not returning your library books means you are a thief who has no intention of returning them until someone points out that you are a thief and you try to wriggle out of it.
Does this help?
This is the point though, you are happy to blindly accept any explanation from Labour politicians that contains the words 'honest mistake', but can't even begin to think that a Tory politician could also make an honest mistake!
Of course I can consider that a Tory Politician can make an honest mistake. Many have. Most of the current senior figures however are far more duplicitous than that.
Have you ever heard the story of the little boy that cried wolf? It doesn't mean that there isn't a wolf, it just means that because of overt past behaviour we tend not to jump straight up and go "there must be a wolf!". If you walk around screwing the public, feathering your own nest and shafting the economy, don't expect to be held in high regard.