Just to make a wild obvious guess, I suspect the change from Bruder(?)
to Stinson was prompted by cost and reliability.  The Stinson organs
are (relatively) inexpensive to purchase and require little maintenance
and can be driven by MIDI.  They're also really easy to tune.

Bruder organs, which sound great to my ears, require an operator to
feed the music books.  They also suffer the usual problems associated
with antique mechanical things.

Considering that parks are a business, I would rather see a Bruder
organ replaced by a Stinson or equivalent, than by a CD, amplifier
and loudspeakers.

Bill Finch