Maybe you should find a news source that isn't infowars if you're actually curious why people would think Trump colluded with Russia.
Although, looking straight into the camera, telling them to hack his opponents, reading the hacks a few days later, and then, up until a few days ago, refusing to acknowledge that Russia interfered with the election, seems like a pretty logical red flag to me.
¯\_(ツ)_/ ¯