Fully describing Spelljammer would end up turning the box set into a $169.99 product probably.
Why would it?
Currently they're devoting, what, 64 pages minus however much it takes to introduce new races, mechanics, etc. to the setting? Eberron: Rising from the Last War, in 2019, cost $50 and was 320 pages, so minus 64x2 = minus 128 for the bestiary and adventure would leave you with 192 pages to describe the setting and mechanics.
Inflation since 2019 is below 10% (even though it's been wild), so at most you'd expect to pay $55.
Instead we're supposed to pay $70 for a fraction as much material.
Again though, the price is something of a red herring - albeit $169.99 is a particularly ludicrous red herring, how many pages is that for, 1000? It don't know if even in 2E there were 1000 pages of setting material for Spelljammer. I doubt there were 400 even (setting material, not adventures).
The point is trying to cram an entire setting into "less than 64 pages" (esp. as it might be a lot less) is tough, and totally unnecessary, given that they're charging more than a 320-page book for 192 pages, and devoting only 1/3rd of them to a mix of setting and mechanics. Again, if, as in 2E, 64 minus pages was "only the beginning" of support for the setting, it wouldn't be a huge deal - but more likely this is the end of actual significant setting support for this setting for 10-20 years. I don't think it's unreasonable to expect a more thorough treatment when a setting is covered that rarely.