Macbook Pros have had at least two segments in them for a very long time: the base level smallest pro and the 'real' MBP.

The base level has fewer ports / less beefy cpu / less features; right now the 14" M6, but previously dual core, two thunderbolt 13" intel MBPs without touchbar. These are popular with corporate fleets.

The 'real' MBPs have all the ports / beefy cpu / best features / optional bigger screens.

Apple likes its market segmentation but it's not precious about it in the face of big technology shifts. If there's hardware they love and want, they'll try to ship it and sort out the segmentation after.

Why does the screen change anything more than a processor does?

I don’t think you’re making a compelling argument here. Arguably a processor is more relevant to a wider range of professionals than a screen is.