from my understanding and observations
i realise why they are cheaper

it is a common practice that the flagship model is the biggest size able to be mass produced

ever wonder why dell have like soooooo many size
with a difference between them is ~1 inch
well
it is common practice to produce standard size
(in the past 19", 21", 24", 27" & 30")
and with the process so delicate
there bound to be defects
and if these defect happens at the edge, for sure they will maximise their potential revenue
and to just cut off the defect and sell it as a new size

it is not economically wise to cut the 24" defects to a standard 21"
where the still good pixel is still usable

thats why there is like fillers between them

dont misunderstood
there should be no problems with the panel produced from cutting away defects pixel to make a smaller size panel

it is just when they aim for their flagship model
there ought to be some % or rejected parts
and couple with original stock of the smaller size panel
it became a supply and demand situation
where they have to offload the stock faster instead of holding on to them
and during that process, they maximise the possible revenue

"them" here might not be Dell themselves
just as well might be a subcon to dell