1. McConnell didn't want to be the guy who convened the Senate trial and presided over the Senate while it voted to acquit Trump but with a majority voting to convict (including 3-4 Republicans). In this scenario, Republicans who might have voted to convict Trump (including sh!tbags like Romney and Murkowski) can play the role of martyrs by simply refusing to convict on the grounds that the President is no longer in office.
2. McConnell wanted a trial but knew he didn't have enough time to do it the right way.
RE: I think perhaps it’s the other way around. I see two possible alternative scenarios:
Either way, the impeachment was pointless political posturing. If the intent was to remove the President from office, then it achieved nothing.
If the intent was to SHAME the President, then it simply backfires. Most people who see (other than the TDS Democrats) this know that it is a unprincipled sham and it is the Democrats and Pelosi who ended up looking like the lawless, vindictive, totalitarian asses they are, and it will go down in history as such.
That seems plausible.