Let's assume your floor is really, totally, flat - to some absurd degree of precision.
Guess what! Your tiles are not. They are nominally flat, but have slight deviations due to the realities of firing ceramic objects, etc. And the larger they are, the more that's true.
They'll likely crack due to inadequate support, but you can lay them down and wait for that to happen, then pull them all up and put down thinset, if you bought enough spares to replace the cracked ones. Or you can just put down thinset to properly support them from the start. Tile is very brittle and cracks easily if not fully supported.
If you really wanted to waste a lot more time, effort, and money than using thinset properly will take, I guess you could grind the floor to some absurd degree of precision and also grind each tile to the same absurd degree of precision. Nobody does that. It's a waste of time, effort, and money. Thinset takes up the minor deviations in floor and tile and supports the tile well as a result.
Or, you could use a different flooring material that's designed to be installed "floating" rather than stuck to the floor.