Why are many painters of ancient people's congresses great calligraphers?

It should be said that many painters in ancient times were literati. They are not only calligraphers, but also have profound attainments in all aspects. So this should only be their identity, which should be the main aspect. In other words, it is not that there is any connection between the two, mainly because ancient painters and calligraphers are all literati, so these are their identities and can be understood as their hobbies. Unlike now, it may be specialized in one aspect. Ancient people generally studied all aspects of art, so it is not surprising that some people may be calligraphers and painters.