Well, the difference between laptops and desktop systems is that desktop processors draw more power than their laptop counterparts, so electromigration at those 90C+ temperatures isn't really an issue in mobile products. You're talking about 95C on a <45W part pulling little current vs 95C on a 5nm 200W part pulling a lot of current.
I'm not sure if your comment on a smaller node = a higher thermal tolerance is correct. Just looking at microprocessors from a high level, you have denser transistors that are physically smaller than older nodes. If the transistors are smaller, then current boundaries should scale with the decreased node size. Pushing the envelope will increase the risk of electromigration if the increased thermal density cannot be cooled adequately - and that's exactly the issue that people are debating now. 5nm is a dense node, the IHS is thick, TDP is up from Zen 3, so the result are high temperatures.
In the end, a good percentage of interested consumers are not comfortable with their processors running that hot, even if it is only a few cores hitting those numbers, and it could have been prevented. AMD could have decreased IHS thickness to aid in more efficient heat transfer, but they opted to maintain AM4 cooler compatibility instead. They could have dropped TDP to 125w and kept 95% of performance while having drastically lower temperatures. My guess is AMD pushed these to the limit because of Raptor Lake, so we'll see how that goes in a few days.