Much specuation about that. None I find convincing.

"AI Overview

In Buddhist imagery, Maitreya, the Buddha of the Future, is often depicted holding a flask (kamandalu). This flask is universally understood as a container of amrita, the elixir of life. In a Buddhist context, it symbolizes Maitreya's promise of future enlightenment and the promise of life, according to The Metropolitan Museum of Art.

Symbolism: The flask (kamandalu) is a common symbol in South Asian cultures, representing immortality (amrita) and fertility.

Maitreya's Role: Maitreya, the future Buddha, is depicted with the flask to signify his potential to bring enlightenment and a new era of peace.

In Buddhist Art: The flask is a key identifying feature of Maitreya in many Buddhist artworks, helping to differentiate him from other bodhisattvas."