I’ve used quite a few hardware dev kits in my time. These early dev kits are prototypes —- released long before the hardware or industrial design is finalized. They are made in small batches, often by hand (with bodge wires everywhere), and are highly optimized for disassembly, debugging, and troubleshooting. They often have tons of ports.

Early Xbox 360 dev kits were literally a PowerMac G5 with some customizations. Early Dreamcast dev kits were in a mini tower case. Frankenstein appendages are common especially for exotic hardware. I remember using an early Haswell dev kit which was a huge plexiglass monstrosity with a capacitive touchscreen glued to the top. (A later dev kit had a much more manageable iPad-like form factor.)

As you can imagine these dev kits are expensive and rare. The hardware manufacturer will want these early dev kits they loan back, and they are almost always destroyed. (A few may slip through the cracks which is how unicorn find like the Nintendo PlayStation prototype was found a few years back.)

As the hardware coalesces and goes through the various development stages, subsequent dev kits typically become smaller and more manageable. In some cases they may be nearly indistinguishable from retail hardware without closer inspection.