Almost no serious orchestras play encores at their home concerts.  However,
in recent years, soloists have occasionally been invited to play a short
solo encore after their concerto; but I remember Menuhin scandalizing
everybody by playing unaccompanied Bach in Carnegie Hall after a concerto
with the NY Philharmonic.

That's my recollection from 50+ years of concertgoing and 40+ years of
conducting professionally.

Please do not search for obscure motivations.  Roger Lebow's explanation
is as good as it gets!

Tour concerts almost inevitably have an extramusical aura into which
encores fit, but even then, when they are part of a regular series
 [Philadelphia, Chicago, Cleveland or Boston playing several times per
season at Carnegie, for instance], I would't expect it to happen.  However
Barenboim surprised us all by playing the Adagietto from Mahler 5 after
a much-applauded Mahler 7th with the Chicago Symphony.  Personally I
liked it better than the 7th.

And foreign orchestras often bring with them pieces which nobody else
more idiomatically--not merely the Vienna orchestras playing Johann
Strauss, but e.g.  the Danish National ripping into the Nielsen "Maskarade"
overture or a Czech orchestra playing "Bartered Bride" or Dvorak Slavonic
Dances..

Joel Lazar
Bethesda MD