Funny, I much prefer a full-size Right-Shift key, which usually requires compact up/down arrow keys. I hate typing on keyboards with tiny, stunted little right-shift keys. I use Right-Shift much more than the arrow keys.
This, in turn, is a trade-off for manufacturing. It will increase the cost of everything slightly. The keyboard unit itself as it will be larger, maye be harder to produce. Machining or producing the chassis now requires accounting for an additional cut.
This is all solvable, yes. Though it is harder for smaller scale productions. It is likely they are working with vendors that, themselves, only have "entirely rectangular" keyboards as this is what the market ends up wanting for cost reasons.
I think the asymmetric, row-staggered layout that keyboards have discourages this.
Though, a fancy technique many keyboard-enthusiasts will use is to have dual-use keys. e.g. Tap-Hold dual use. The key acts the same when tapped, but acts as a modifier key when held.
e.g. changing Capslock key to escape when tapped, Ctrl when held is probably the easiest to think of.
The best use of tap-hold is for Home-Row modifiers. Putting alt/command/ctrl/shift as modifiers of asdf (and symmetrically, jkl;).