[dredmorbius]

FWIW, I learned a few things researching my answer.

(A prime validation for answering questions, BTW.)

My first read was that the old-school ramfs / ramdisk limitations still held. I can't actually even find documentation on them, though I'm pretty sure I'm not dreaming this.

Circa 2.0 kernal IIRC, possibly earlier.

OK, some traces remain, see:

https://www.tldp.org/HOWTO/Bootdisk-HOWTO/x1143.html

Note that this is OBSOLETE information.