I would also never buy such a machine. Still, in 25 years of owning my own computing resources, I have never actually expanded the internal storage of the 6-8 systems I've built.

IME, expandable storage in Macs was mainly used as a run-around around the Apple Tax on their storage options - buy the base model and upgrade the storage yourself for 1/3rd the price.

I always thought it was a fair trade-off. Pro users who care more about stability/support can pay the Apple Tax, and enthusiasts on a budget can DIY it and get a better machine for less. It feels like greed to cut off that path.

It was also way more important in the day of spinning disks - so many machines from that era got a new lease on life by having the HDD replaced with an SSD. Imagine if HDDs had somehow been soldered in...

Yeah, I was really hoping this would take M.2 sticks.

wouldn't a prosumer actually opt for a NAS with fast gigabit or better network speed?

For a prosumer there’s only so much you can offload to iCloud or NAS and eventually these machines, which are typically owned for a long time, do run out of space.

Apple added back expandable internal storage for the Mac Pro and I hoped they would relent here too