That was actually feed back given from the US army to the development team at Heckler & Koch.

The rifle evolved form the kinetic energy carbine portion of the doomed XM29/OICW program, and eventually became the G36 rifle. In between those two, however, it was the XM-8, and it came close to adoption by the US military.The XM-8 was designed to be a very modular system, with a variety of interchangeable stocks, handguards, optics and accessories.

Video: [16:54] https://youtu.be/Te2IqFbRR7A?si=

https://www.forgottenweapons.com/hk-xm-8-what-was-it-and-why-with-larry-vickers/

https://www.forgottenweapons.com/almost-adopted-the-hk-xm8-family/