Asgore never wanted to be king, he just wanted to be a gardener.
Asgore talks about how he never wanted power or control, he just wanted to make people happy and bring hope. At the start of the game Papyrus mentions how Asgore will trim a hedge in the shape of his face, and in the true pacifist ending we find that to be true. You see, Asgore loves plants and gardening, as you learn from monster kid when they talk about how Asgore offered to bring in his flowers to help teach kids how to care for them and learn about responsibility.
On neutral or pacifist route you find a note in new home about him being out weeding in the garden. You finally meet him while he waters the golden flowers in the throne room. On genocide route you find him talking to Flowey, remarking how strange it was and how he never saw a flower cry before, he wasn’t finding the flower talking to him strange, it was the emotions and crying that he had never seen. He must know about echo flowers, which makes sense based on how much time he spends walking outside, which is what he suggests the human do when you first meet them.
The energy pitchfork/ doubled edged scythe thing he uses to fight has three different theories/reasons why he has it as a weapon. First reason is because a red pitchfork completes the Devil allegory, what with the horns, being a giant goat man with a beard, and being a king of monsters living in the underworld that wants to steal human souls to free his monsters. The scythe bit (when his eyes flash blue and orange in the order of his swings, you can sort of see the weapon is held and used like a scythe during that attack) probably helps with his allegory as death, a dark cloaked figure with a scythe waiting at the end of your journey, telling you to only return when you have finished all of you unfinished business, and then tries to reap your soul. The second theory is that it is because Asriel was killed by villagers using farming tools, likely pitchforks and scythes, although he is shown in the intro having it during the war against humans, but we don’t know if that’s just supposed to show he fought in it. The third theory is that he likes landscaping, gardening, and farming, and that’s what he uses the energy pitchfork / scythe attack outside of battle.
In the pacifist ending he gets his dream, no longer having to be a king to keep peoples hopes up, no longer needing to fight and kill, he can raise spirits the way he always wanted to, by gardening and making skeleton topiary!