Why is plural of cello not celloes?

The word "cello" comes from the Italian word "violoncello", which is a diminutive of "violone", meaning "large viol". The Italian plural of "violone" is "violoni", and the plural of "cello" is therefore "cellos". The English plural "-es" is added to words of French or Latin origin, but not to Italian words. There are many other Italian-derived words, including:

- solo- the plural of which is 'soli'

- piano- the plural of which is 'piani'