Great answer FF
Or…OOOOOR…
Also, some pianists are called maestros when they get older and more renown.
Some pianists are virtuosic but not necessarily renown for that particular quality, and so they are not maestros.
Other pianists are virtuosic and have a certain musical quality that they are renown for (their artistic touch, etc) and are therefor maestro.
Conductors are maestros because they have high levels of musicianship and have a very idealistic vision in performance. In contrary, virtuosos can be virtuosic on one instrument, a master of their own instrument but have not necessarily have lots of experience in any other musical avenue.
I would much rather be a maestro.
When I hear the word virtuoso, I think of someone with skills that are unparalleled by any other living human.
When I hear the word maestro, I think of someone who is more mature than a virtuoso. Like a maestro is something virtuosos become.