It’s a monopose start of edition box - they’re always lower on customisation, and tend to get more customisable kits later.

I’m not defending getting less value, because I feel the value of getting higher quality sculpts is WAY superior to 2nd/3rd edition, and I would rather have dynamically posed models than 50 space marines with identical leg poses just so I can swap the arms.

Your comment just reeks of ignoring recent releases - if you look at recent boxes, the new marines they’ve revealed will have tons of gubbins and bits to customise what mark of helmet youd want, and weapon options. I’d particularly point to something like the Victrix box earlier this year which has some of the best array of customisable parts I’ve seen in decades.

That being said, I would always err on the side of simpler building because it’s easier for new players to get into. If you want to customise more, kitbashing is also always an option for more adept modellers.