My guess is because members came to Johnson and told him he didn't have the votes to pass it. At least not bundled. Perhaps also because aspects of that vote may be inconsistent with the "big beautiful bill". Or at least, some members wanted to deal with the latter before the former.
Or perhaps the opposite. Aspects of that vote may coincide with the Big Beautiful Bill.
It has been said politics is a blood sport, imagine a football game where the plays were open for group discussion even after the quarterback called what the coach sent in. Not many would pay to watch.
A vote cancelled is a vote squandered.
Strike while the iron is hot.
Nike - Just do it.