I'm having trouble trying to articulate my thoughts on your first question, but here it goes:
Remember first of all that kamma is volitional action, not the results. The results of kamma are the fruits of kamma, or Vipāka. It's a small note but it helps to be clear.
Because we live in a creatorless universe, there is no overarching intrinsic, deontological essence of moral worth to an action. There is no universal good or bad declared by a God or Supreme Being. There is only cause and effect; some actions have results that generate generosity, compassion, and wisdom while other actions have results that generate greed, hatred, and delusion; the former are the roots of all joy and the latter are the roots of all suffering. Murder is wrong because as an action it generates mindstates that lead to suffering. That result, whether mental or physical, is the fruit of the kamma, or volition, that led to the action. If an action (kamma) did not lead to an unwholesome (i.e suffering-generating) result then the action could not be an unwholesome action.
To use philosophy language, A iff B, or: An action is wholesome (moral) if, and only if, its result is a wholesome (moral) result. So asking "Why are the fruits of wholesome kamma also wholesome?" is a little like asking "Why are all bachelors single?" in that the moral nature of an action can be defined by its result, in the same way that someone's status as a bachelor is dependent on their being single. You can't say, "This action was moral but the result was unwholesome" any more than you can say, "This person is a bachelor but he is married."
In Buddhism, wholesome behavior is that which leads to the end of suffering. If its result is unwholesome, then by definition the action could not have been wholesome because it did not lead to the end of suffering. When viewed this way, the universe does not seem moral but instead just logical; wholesome action = wholesome result.
I hope this helps! It's just my view of the matter, I hope I have not made any errors. Please do correct me if I am wrong.
Gain and loss, status and disgrace,
censure and praise, pleasure and pain:
these conditions among human beings are inconstant,
impermanent, subject to change.
Knowing this, the wise person, mindful,
ponders these changing conditions.
Desirable things don’t charm the mind,
undesirable ones bring no resistance.
His welcoming and rebelling are scattered,
gone to their end,
do not exist.
- Lokavipatti Sutta