Why is market absorption of issued US Treasury Bonds (with the Fed purchase plan) a problem?
Why can't the Treasury and the Federal Reserve agree upon a controlled issuance and instant procurement of UST bonds &quot;straight from the printing press&quot;?

Treasury bonds are not “printed” at a “printing press,” the only “printing press” is run by the U.S. Mint, where they print Federal Reserve Notes (e.g., dollar bills). Treasury Bonds/Notes/Bills are sold at auction.
Not sure of the exact statute that forces this, but the Federal Reserve does not bid at auction, they buy in the secondary market. This answers your question.
Update: a FAQ on the Fed website: link.

Why subject the market to the ambiguity ...

Because there is no legal alternative, other than changing Fed operating procedures to having them cap bond yields. (One can search for discussions of “yield curve control” for more details.)
As for financial market commentary, it is not always reliable, so statements made there need to be taken with a large grain of salt.