So to be clear, I fully understand that the german kingship was elective but it still followed dynastic favor.
After Henry died, he had both a young son and a younger brother, the Hohenstaufen House was secure but the Welf Otto jumped in a gained a small but important support base with the Archbishops and contested young Frederick and Philip's claims.
And from that moment on, Otto did jack shit, it seems. Philip rallied support, converted Otto supporters, defeated Otto in battle and was nearly to uncontested kingship when a Mad Count murdered him.
Then everyone happily switched to Otto, elected him King, and Otto had a lackluster rule, got his ass kicked by the French and was eventually deposed for Frederick II of house Hohenstaufen.
What was Otto thinking? why did anyone support him in the first place besides countering the power of the Hohenstaufens? His attempt and rule feels like a bad farce.
I actually know this one, nice.
So you have to understand that the Hohenstaufen family was pretty strong in Germany and with the marriage to the Hauteville family they also had the south of Italy. This unsettled some German princes that really didn't wanted Frederick on the throne of Germany.
When Herny died in 1197 his wife Constance of Hauteville, Frederick's mother, was still alive and dreamed of distancing herself and his son from the German Empire. She made him renounce to his claims on the Imperial title and crowned him king of Sicily. This was possible with the help of the newly elected Pope Innocent III who worried a possibility of the Kingdom of Sicily unifying with the Empire, therefor flanking his state both from north and south. Constance died in 1198, not after removing most Germans from his court in Palermo, and innocent became the tutor/guardian of a young Frederick, he was only 4.
Now Germany was without a king and the position was free real estate. Otto got a pretty good shot when his uncle King Richard Lionheart of England supported his claim. The possibility of a Welf being Emperor scared some princes that sided with Philip, it was a weird situation when you think that neither of them had a very strong claim. At some point Innocent started favoring Otto's side since Philip didn't like the influence that the Pope had over the Kingdom of Sicily and refused to consider it a "territory under papal control". Also Otto become very dependent on the support of the Pope when his uncle died, losing England as an ally.
An important part of this story is that Innocent never really supported Philip because of the Kingodom of Sicily thing until 1206 when he won against Otto. In any case it didn't matter since Philip died in 1208 and Otto was crowned Emperor in 1209 after marrying Philip's daughter making peace between the two sides.
Otto made some promises to the Pope during all this years of war but now he was the Emperor and maybe though that he could get away with more than he actually could. He tried to retake some territories that the Pope hade in central Italy and planned an invasion of Sicily to annex it back into the Empire. This angered Innocent who started looking for another Emperor. The only candidate was Frederick, who was now 16, which was a problem for the Pope since he just finished fighting this family to take the Empire from them and also this would mean be surrounded by Hohenstaufen territory yet again.
He made the young king promise to keep the two titles separated, nominate his son King of Sicily and only after that supported his claim on the Empire with the help of some German princes and the King of France. Otto was overwhelmed and lost his title and after Innocent death, Friederick took back his place as King of Sicily which angered yet another Pope and ultimately lead to the conquest of the Kingdom by the Anjou dynasty and the rebellion of the island of Sicily in favor of the Crown of Aragon which would formally divide the Kingdom in two for centuries to come.
Sorry if I made some typos, I'm not an English speaker