The first requirement of the Forbidden Jutsu: Soul Reincarnation Technique was a body with an extremely high degree of compatibility with the deceased's soul.
Furthermore, while performing the forbidden jutsu, a massive amount of life force had to be infused into the body. Only members of the Uzumaki Clan, the Senju Clan, or those possessing Yang Release Chakra could attempt it.
The second requirement was a method to summon the deceased's soul, and the Spirit Body also had to be equally complete and powerful.
The third requirement was an extremely extensive knowledge of medicine, as well as a certain understanding of magical knowledge from the New World.
Aside from the conditions for using it, there was also the price the caster had to pay.
Like forbidden jutsu such as "Izanagi" and "Rinne Rebirth," the more powerful the technique, the greater the price that naturally had to be paid.
After reviving the dead with the Soul Rebirth Technique Yoru Machi had developed, the caster would lose a portion of their soul power as the price of their transaction with the God of Death.
Moreover, after restoring the deceased, the caster would permanently lose an amount of Chakra equal to that of the resurrected person.
In other words, the greater Minato and Kushina's Chakra reserves, the more Chakra Yoru Machi would lose in reviving them.
When they learned of the price required to revive them, Minato and Kushina repeatedly tried to persuade Yoru Machi to stop. Being able to remain by his side in their current Spirit Body states was already quite good enough.
Although Naruto might not be able to see them, they could at least watch their son grow up healthy.
The price of losing part of his soul and permanently reducing his Chakra reserves was far too great. Minato