They know they’ll never get Biden removed. Even the craziest Republican in the House realizes that the impeachment would die in the Senate. This is purely being done for three reasons.

First, it’s payback. Trump was impeached twice so they think they are “owed” at least one impeachment. This is especially true, they feel, because Trump wants to see Biden impeached and they must follow Trump or else.

Secondly, it’s an attempt to make impeachment meaningless. If they impeach Biden over nothing, they can claim that impeachment is a purely political process and Trump’s two impeachments mean nothing.

Finally, it’s a way for them to “prove” that Biden is corrupt. After all, he was impeached, so this means that he’s done illegal stuff. Note: This conflicts with the second reason, but they don’t care. They’ll argue that Biden’s impeachment means he’s corrupt, while also arguing that Trump’s impeachment proves that impeachment has no meaning.

Removal isn’t the goal. They’re just looking to score political points. The smarter Republicans realize that this could cause a massive backlash (ala Clinton post-impeachment), but the smarter Republicans aren’t the ones with their hands on the wheel.