Why are photos square and not round?

I know that camera censors are rectangular with different dimensions and sizes for different brands and models, but why can't they be designed as a circle instead?

The light that shines through the lens falls in a circle over the censor anyway and some parts of this circle is not currently used due to the censor crop factor.

For instance, we can have round censors and then view all the photos round on our computers too, we can print photos out round and frame them in circular frames.

I just don't understand why we still have to adhere to rectangular censors and photos just because the first film cameras had rectangular frames.

Can anybody add some colour to my round thoughts?

Thanks
Jacques
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'A camera is a device that helps one appreciate the world without it.' - Jacques

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