The Infinity Gauntlet was not the only badass artifact in the multiverse.
The Cosmic Cube and the Heart of the Universe were likely even more powerful than the Infinity Gauntlet.
Actually, he could be more confident and remove "likely."
There was more than one Cosmic Cube. As long as the conditions were right, they could be created.
First, a special, sufficiently stable energy field had to be formed. Then, a rift had to be opened into the Beyonders' extradimensional realm. Energy from that dimension would flow through the rift into the field. Once the energy field was filled with extradimensional energy, it would transform into a perfect cube.
In other words, creating a Cosmic Cube required going through the Beyonders.
Simply put, powerful Cosmic Cubes were nothing more than toys to the Beyonders.
From the information left behind by his grandfather, Kronos, Thanos had learned of the Cosmic Cube's existence and location. Within the Beyonders' dimensional realm, the Beyonder—the infant form of the Beyonders—had left behind a Cosmic Cube.
With the Cosmic Cube, its holder could turn the desires in their heart into reality: from controlling elements to manipulating time and space, transcending logic, and more.
Since he had given up on the Infinity Gauntlet, he needed an artifact capable of contending with it, perhaps even surpassing it.
Thanos immediately thought of the Cosmic Cube.
Thanos's grandfather had been the ruler of the Eternals, the god of time who wielded the laws of time with mastery. By using those laws, Kronos could create a temporal vortex in which time endlessly repeated, a phenomenon spoken of across countless timelines.
Sound familiar?
Doctor Strange could do it as well, but he needed the Eye of Agamotto.
Kronos, however, could accomplish it through his own power alone.
In terms of strength, Kronos had