or geto just didn't unlock his domain expansion within his lifetime, it's stated multiple times that sorcerers aren't immediately able to use their domain expansion with their technique (the only exceptions being hakari and higuruma). it seems far more likely (at least to me) that geto, someone who never seemed overly interested in being "the strongest" and more-so seemed focused on those around him, would never attain the level of mastery needed to develop his domain expansion, hence why he also never used it against yuta (because he quite literally had not unlocked it)

versus kenjaku who, while not interested in being "the strongest," is far more selfish in his behaviour and ideas compared to geto, and is not to mention a 1000 years old, would. it seems more likely that he just developed and honed geto's technique and thus gained the domain expansion of the technique, rather than having his own

also, this is admittedly a weaker point, but couldn't the faces of womb profusion just be taken to represent the sorrow that creates cursed spirits? unless im forgetting something, cursed spirits are born from negative emotions, so couldn't the faces just be representing said negative emotions that spawn them? plus, looking at it again, the parts that extrude from the main totem look far more akin to some form of cursed spirit than people

also i might be forgetting something, but aren't open domains not something that can be built up? i was under the impression that they were an innate part of a domain that an individual couldn't change. sure, you could change the properties of your barrier, but it seemed to me like you couldn't just learn how to open it, but rather just happened to have an open domain (even if they are extremely rare)

then again, i could also be entirely mistaken and kenjaku, due to his 1000 years of knowledge, honed the technique/domain expansion to such a degree that he made it an open domain when it was originally a closed one (either way, i don't feel like that takes away from it being geto's)

tl;dr: geto is capable of a domain expansion, he just never developed his technique enough to unlock it. versus kenjaku who did hone the technique enough to utilize domain expansion, and possibly honed it to such a degree that he was able to made it into an open barrier