Because they were commissioned and paid to do so.
The Last Supper is the last meal Christ and his disciples had together.
Hundreds of artists through the ages have painted the 'Last Supper'.
If you mean Leonardo's painting (because lots of other artists have painted this subject) it was commissioned by the Duke of Milan.
last supper
A Renaissance painting.
The Last Supper
None
The Last Supper
Christian religious art.
the last supper and The Vitruvian Man
the last supper
Leonardo da vinci