I have no dog in this fight but maybe it's cuz there is no gravity? I don't know and personally I don't care if there is or isn't gravity. It's not going to change anything.
So - pick up an object and then let go.
Why does it fall to the ground?
This definitely happens - and it needs to be explained. Sir Isaac Newton saw an apple fall from a tree (I've actually sat under that very tree!) and wondered exactly this.
Why did that happen?
That's the question here. Round Earthers (and every physicist on the planet) agree that there is a force (or, arguably a 'pseudo-force') that pulls small objects like apples towards large objects like planets. This is what makes the sun, stars, planets and Earth round - it's what causes orbits to happen - it explains why we have seasons and day and night. It explains tides and that you weigh a little bit less if you're at the equator than at the North Pole - and a little bit less if you're on top of a large mountain. It explains galaxies and weird shit like black holes. Every experiment ever done to examine these things has ended the same way: GRAVITY.
But in a flat earth, there is a bit of a problem. Gravity wouldn't exactly work like it really does. The effects are subtle - but important if you actually care whether your ideas about the shape of the Earth are right or wrong.
So intelligent, thinking people must look at this discrepancy between what we claim to be true and what we can actually measure (and can easily see with our own eyes in the case of things like tides).
When you open your eyes and truly THINK about the world around you - rather than following some dogma in a sheep-like manner - you come to the inescapable conclusion that Sir Isaac Newton was *almost* 100% correct - and with a small tweak from Albert Einstein - we now have an answer that seems to reproduce reality PERFECTLY. That answer is NOT the theory of "Universal Acceleration" - that theory cannot reproduce many important things that we can easily see and measure.