The money in your checking account is still available for lending. Most every dollar on deposit with a "bank" remains available for that bank to use/leverage/loan. Money isn't really parked until you stash it as cash under your mattress.

> Wouldn’t withdrawing from your 401k and transferring it to a checking account limit the pool of funds available for equity investment and move it into lower risk assets

Yes, at the margins. But these are still financial effects. When a capital project is delayed because the bank they hired to sell stock came back with a lower price after talking to the retiree’s asset manager, that’s a real effect.