Profiteering, not price collusion - corporate profits from 1980-2020 accounted for around 10% of price increases, whereas they account for more than 50% since 2020.
As for why it didn't occur under Trump, it's because he created the conditions that allowed it to happen but was run out of office due to his bungling of the pandemic. He cut corporate tax rates making it cheaper to remove capital from the system than keeping it in, started a bunch of stupid trade wars that increased taxes on American consumers in the form of tariffs on the raw materials and finished goods they were purchasing, and then bungled the pandemic response and ground our supply chains to a stop.
Since we've emerged from the Trump economic crisis, the market and corporate profits have been at all time highs, but since the monetary supply has been in decline for more than a year, those profits have only been sustained through wage cuts and price increases.