They don’t actually believe it’s treason; They’re trying to water down the word, so when Trump gets charged they can go “but look at all the “treason” the Dems have committed! The Dems haven’t been punished for it, so why should Trump?”
It’s a pretty common conservative tactic. Any time a prominent party member is going to be charged with something or have some big scandal break, they start rabble rousing and accusing liberals of whatever that particular key word or phrase is. All to dilute the actual meaning, and be able to go “it really isn’t that bad because the Dems do it all the time.” It doesn’t matter whether or not the democrats actually did any of it; All that matters is that republicans say they did, and conservative voters don’t fact-check them.