About shorter keyboard space bars

Did you know that the Macbook keyboard layout has a shorter space bar than a "standard" keyboard?

Shortening the space bar is a common choice on smaller keyboards, especially on laptops, because it leaves more space for the cursor keys (the "arrows").

On the Macbook keyboard there's a really interesting side-effect of this approach: it moves the two Command keys closer to the center of the keyboard.

It might be because I have small hands;
It might be because I use the right Command key a lot;
It might be because the Command key is the most used key for shortcuts in macOS;
...But I noticed that, even if we all hate it, I feel more comfortable typing on the Macbook keyboard, and I'm pretty sure it's because of the space bar alone.

Once I realized that, I started to wonder:
Why is the space bar so big on most keyboards?
Do mechanical keyboards with a short space bar exist?

According to Wikipedia it seems to be mostly for historical reasons, because they were mechanically different than the rest of the keys and needed more force:

Originally (on early writers dating back to the late 19th century) the "bar" was literally a metal bar running across the full width of the keyboard (or even wider, and even surrounding it) that triggered the carriage advance without also firing any of the typebars towards the platen. Later examples gradually shrank and developed into their current more ergonomic form as a wide, centrally located but otherwise apparently normal "key", as typewriter (and computer) keyboards began to incorporate additional function keys and were more deliberately "styled". Although it varies by keyboard type, the space bar usually lies between the Alt keys (or Command keys on Macintosh keyboards) and below the letter keys: C, V, B, N and M on a standard QWERTY keyboard.

Interestingly enough, some countries use a shorter space bar. For example in Japan the space character is not used much, so the standard Japanese layout has a space bar even smaller than the Macbook one:

I spent quite some time looking for good mechanical keyboards with a short space bar:

• xahlee.info: Tiny Space Bar on Japanese Keyboards
• geekhack.org: On keyboard design philosophy: Small space bars.
• overclock.com: Recommend keyboard with small space
• deskthority.net: Small Spacebar Keyboard

Here's a quick recap of the available options that I've found so far.

The only mechanical keyboards I've found that are built with a short space bar are the Filco Majestouch Minila Air:

And the Ultimate Hacking Keyboard, which is a composable split keyboard that can also be used in a standard way:

Following the Ultimate Hacking Keyboard trend, you could also make the jump and join the split keyboards world, which offers a sensible amount of options for short (or just "different") space bars:

The most time (and money) consuming solution is probably building your mechanical keyboard from scratch.
I'd love giving it a try in the future... but I'm not ready for it yet.

I still haven't decided which keyboard would suits better my workflow and if I should pull the trigger on a new mechanical one.

For now, as a temporary solution, I (sadly) stopped using a top-notch mechanical keyboard that has a big space bar (Varmilo VA87) in favor of a compact Apple Magic Keyboard.
I know, it has a horrible key-travel, but at least it uses the same layout used by the Macbook keyboard and I don't have to do weird thumb movements to reach the Command keys.