The new iMac uses a 143W power adapter. Apple couldn't reduce M1 power to 100W to charge it using USB-C PD.
It's basically just a Mac Mini but with a screen, keyboard and mouse/trackpad and a monitor. Should be under 100W easy. There's certainly another reason for it. Maybe just to get rid of an enormous stock of power bricks (so much for environment)... I do like the ethernet port on the power brick though, hope they put that on the next MacBook Pro.
The new iPad Pro still includes a power adapter in the box. Only iPhone team cares about environment, but wait, they are still using Lightning instead of USB-C.
Yeah Lightning royalties are still very valuable... Also, the 143W power brick could be in preparation for an iMac Pro latter this year. That one will certainly have a more powerful M1 chip, 6K screen and possibly come with in house dedicated graphics. Hence more power needed. So it makes sense cost wise to only produce and use one model of power brick. Though why didn't they put the Rj-45 on all bricks? Looks like another greedy product segmentation...