You answered yourself, it’s because Republicans need to lose consistently, and it’s been over 70 years since the last time they even lost three consecutive terms.
Meanwhile, did you see what happened after three consecutive Republican terms? Clinton. Reagan + H. W. in a row definitely shifted the overton window to the right, and forced Dems to react accordingly. That’s what needs to happen, in reverse. Allowing Trump in office again would send the message that racism is the winning strategy, and Dems might get even worse.
Waiting for the window to shift might look like a pie in the sky to you (and you’re not even that wrong, considering how the DNC keeps pushing their worst), but a third party winning is a pie in straight outer space.
And splitting the votes of the sane Americans among multiple parties, allowing Trump to get a second term and enact Project 2025 is a productive and thought-out strategy?