Reading between the lines it looks like Meteor Lake desktop will be the lower power, lower performance desktop chips. Arrow Lake desktop looks like it will be the power powered K overclockable chips. They would be in totally different market segments even if they are both desktop chips (It isn't like I3 and I9 chips are competing for the same customers). I have not seen any confirmation of that, but all the tea-leaves seem to be pointing that way.
Why do it? De-risking. Intel has already announced that they will be overlapping products for that very reason. They were burned badly by putting all of their eggs in one basket that failed to be work well (10 nm). They are very deliberately going down multiple simultaneous paths to de-risk and avoid that situation from happening again. The counter argument is that going down multiple overlapping paths is costly. That is true, but only to a certain extent--Intel does not seem to be duplicating every die combination on different nodes.
Take Alder Lake for example, there were 4 different Alder Lake dies. (1) 8P+8E desktop, (2) 6P desktop, (3) 6P+8E mobile, and (4) 2P+8E mobile.
https://en.wikipedia.org/wiki/Alder_Lake#Dies It does not appear that Intel is making 4 Meteor Lake dies and 4 Arrow Lake dies. But instead, Intel is probably making a smaller number of dies on each node. That way, there isn't as much duplicated cost. But they still get to de-risk in case one node is delayed or is an outright failure. They will still have desktop chips to sell in that case.
So think of Meteor Lake desktop and Arrow Lake desktop as the two different desktop dies that Alder Lake had. A lower powered, lower performance one. And a high performance one. Plus, it gives Intel a great option to include different mixtures of the other chiplets. Maybe the K high-powered chips don't need as much iGPU performance as those would often be paired with a discrete GPU.