Obama was also a consummate professional politician.
He chose his words carefully. He didn't spout hateful nonsense every chance he got.
So, in Obama's case, you could mock his lack of achievement (fair enough) but he didn't provide constant opportunity for mockery by saying and doing ridiculous things.
Can you imagine, for example, Obama bragging about how big his nuclear button was? No, he would have said something very statesmanlike and made a sincere face while he was saying it.
I'm not a big fan of either Obama or Trump. But Trump certainly deserves all of the mockery he's got coming to him.