Why do people think NASA is lying about the shape of the earth? What would be gained by lying ?

Psychologically the reason people say that is because having unusual beliefs is a way of bonding with each other and feeling like you're in a special in-group who is better informed and more intelligent than everyone else. The ostensive reason is that NASA are part of a global scientistic mindset whose purpose is to make people feel insignificant so they are not religious and are able to be manipulated into materialism and consumerism.

However, obviously Earth is (almost) round.

Why do you think NASA has an opinion? It is only there to launch things and monitor them.

Nothing

Absolutely nothing

Nada

Zitch

Naff ***

Some people are stupid and arrogant; and others are willing to lie if they can make money out of those stupid arrogant people.

"Why do people think NASA is lying about the shape of the earth [sic]?"

Because they are stupid.

"What would be gained by lying?"

As far as I can tell there is nothing to be gained by NASA lying about the Earth's shape. For most of us the shape of the Earth has no impact on our lives. I cannot see the officials at NASA lying in the hope some fool believes them and sails a boat off the edge of a flat Earth.

You mean ,those people that don't think?

There is a world of evidence that the world is a sphere.

And that is not just the fact that I, and millions of other people have flown around the world in airplanes.

We have communication and GPS satellites orbiting the earth. My car uses that technology to show me how to drive to any destination I ask it.

NASA has not - as far as I know - bothered to assert the world is round - it being very obviously round.

Perhaps you could scroll through these photos if you have time

https://www.space.com/20759-earth-from-space-nasa-...

why do you assume that they're thinking?

What people? Most "flat earthers" are just trying to attract attention.

There's a proper descriptive term for such people:

Willfully and proudly stupid.

The knowledge that the Earth is a sphere goes back over 2,000 years before NASA was created.