Why did Japan end almost all contact with Europeans in the early

Europeans had nothing the Japs wanted except guns. Guns were no longer necessary once Japland was united.

To stop Europeans trading with potentially rebellious clans and causing civil unrest.

Japs were autistic xenophobs

Because Christian missionaries were suspected to be the vanguard of a future foreign invasion, this is something that comes up pretty often in the transcript of dialogues with imprisoned missionaries, like for example Giovanni Battista Sidotti.
The shogun believed his suspicions proved true when the rebellion of Shimabara broke. In reality it was a rebellion over taxation and food distribution at a time of extreme famine, but their leader was a young Christian convert and involved Christian damyos as well, so it was unavoidable that he would connect the two things and close down free trades with Catholics. Note that he still held belief that Protestant were able to keep trade and religion separate, so Dutch were still allowed a little more freedom of commerce with the country

Jesuits and other "missionaries" were plotting with converted daimyos to seize power