Sounds like guitar players are the only musicians that have tens of multiples of their instrument. Like, how many drummers have 15 drum kits? Singers maybe have multiple mics, but 10? do violinists, tuba players have 10 different ones? I suspect not, but genuinely I have no idea.
My daughter, a pro, has one cello. Another would be $25,000 to $40,000. You can easily double that. My other daughter, a pro violist has two, the $5000 instrument she played through college, and a $25,000 instrument she bought a year or two ago. A bassoon can be $80,000, a student bassoon $20,000. Brass instruments are very costly too. A good piano? $100,000+. Pure economics dictate what people can buy.
Why?
If we stay focused on the instruments that are typically in a band or orchestra and ignore collectors there is a common progression from student to professional that may or may not lead to multiple instruments. Many students rent rather than own. If talent, economics and interest come together a student may upgrade to an "intermediate" quality instrument. If they don't sell their student quality instrument they have two but the inferior instrument gets very little play time except for parades, football games or other outdoor gigs in bad weather. Players who expect to be professionals often own the best instrument that they can afford but economics usually dictate the lesser instruments need to be sold in order to paid for the gigging instrument. So, as noted, economics are going to drive most players to one instrument. $25,000 can buy several good quality guitars but maybe one good cello.
There are some outliers. A good saxophone player can play soprano, alto, tenor, baritone or bass saxophone. Many saxophone players will own more than one saxophone because being able to show up at a gig with multiple saxes gets them more gigs. A bassoonist who owns a bassoon and a contrabassoon will get more gigs than a player with just a bassoon. Same thing for a trombonist who also owns a bass trombone. The analog may be to a guitarist who also plays bass or mandolin.
Tuba players may have both a tuba and a sousaphone but that means they are playing in several distinct genres.
Some flautists, in addition to a piccolo, will also own flutes made of different materials - gold, silver and wood come immediately to mind - and the choice is based upon tone quality. This might be the closest analog to a guitarist who owns multiple instruments because of the differences in tone-woods. Trumpet players can make similar choices - trumpet, cornet, bugle (for some applications) and flugelhorn.
There is not really an analog to owning multiple guitars for different tunings in the band and orchestra world. Similarly most band and orchestra players do not have a spare instrument that they bring to a gig, "just in case". They have tool kits and lists of people they can borrow from in an emergency.
Guitar owners have functional reasons to own multiple instruments and most of those functions don't have an analog in the band and orchestra world. So band and orchestra musicians are going to spend their money on the best instrument they can afford and not on a second instrument that may not really do anything better and different from the first.
And the economics are huge. We would not be talking about non-collectors with "lots" of guitars if student quality, beginner, instruments were in the $1000-$5000 range with prices going up as quality got better.
