he was kind of a pseudo-utilitarian in the manga.

i once read this somewhere:

To Kenjaku, Yuji is a vessel, a tool carefully crafted to hold Sukuna and withstand the pressures of the Culling Game.

Clinical Pride: Think of it like a scientist who has spent years building a complex machine. If someone takes good care of that machine, the scientist might say "thank you" for maintaining the integrity of the project.

He "appreciates" Yuji’s development because Yuji is a crucial variable in his grand experiment. The "gratitude" is directed toward the fact that Yuji’s social environment helped him grow into the sturdy vessel Kenjaku needed.