For many reasons.
For starters, these two are perhaps the most gifted / natural geniuses that were introduced in the manga.
They reached a power level in a somewhat legit way compared to the ones who are ranked higher than them;
Obito is stronger but is an Uchiha and was given Senju DNA,
Madara is stronger but also was given EMS by his brother
Sasuke is an Uchiha + has now achieved EMS
Naruto is an Uzumaki and was given Kyuubi
Nagato is an Uzumaki + was given the Rinnegan
Kabuto took many powers from different people and thus became overpowered
Hashirama is the ONLY one who is stronger than them and apparently got that stong from having ''senju' lineage
Itachi was an Uchiha but it stopped there, he didnt get Senju DNA, a Bijuu or anything of the sort
Minato doesnt have any bloodline but he did build his arsenal arround Tobirama's technique, but it still takes skills to achieve such perfection
Like i said, they reached such power level without getting gifts / power ups like the ones who are considered stronger than them (except Hashirama), they took what their had to a whole other level because of their umatched genius skills.
Outside of their skills and power, they are put against each other because of how much alike they are.
Itachi is to Sasuke what Minato is to Naruto.
They both gave away their life for them, they both gave them power ups and pretty much ''decided'' Sasuke and Naruto's lives with the sacrifice they made.
Itachi is responsible for making sure Sasuke would exploit his full potential, thus leading to him having the mangekyo, and in the end gave him his own MS to achieve EMS
Minato sealed Kyuubi which powered up Naruto since forever in terms of chakra and power, and Kushina ensured that Naruto would take that power to the next level when she helped him in the tug of war.
They played the same role
THey are imo equally strong
THey were both extremely selfless and humble, to the point its annoying to see how harsh they can be on themselves despite everything they have achieved when reality litteraly shitted on them at such a young age
No other being in this manga can be considered to be as flawless as them, they arent the strongest ones, but given the circumstances and the limits they had to face, no one would have been imo. able to achieve such heights as these two did in their lives.