Easy. Several factors here. (None will be popular here.)
1) Young musicians aren't trying to make money. They're trying to make it big or play whatever "core" music they like. Anything else is a "sell out". As such, many of them have no money. They are paying to play as it is. The school of thought when I was coming up was play something marketable and toss out some originals when you can. That way you make some money while writing.
2) There simply aren't as many people taking up stringed instruments in my view. When I was in high school (mid to late 80s) I would venture a guess that of the 100 or so males in my class, 75 of them had a guitar or bass and more than half of them knew how to play it somewhat. Seriously, I would guess that roughly 40% of the males in my class played guitar or bass. Not so today. Kid next door just graduated high school in a class of around 200. He only knows a couple of guitar players and no bass players. Anecdotal? Yes. Indicative of a shift? Also yes. In the early to mid 90s I kept my bass student roster full at 28-32 students and even had a waiting list at times. The guy teaching bass at the same store I taught at is a guitar and bass teacher. He feels great if he has 5 bass students and maxes out at around 18 combining guitar and bass altogether. And it's not like there are 15 bass teachers here. He is one of only a couple.
3) Live music scenes throughout the country (with rare exception) are taking a dive compared to the 70s, 80s, and early 90s. During those 25 years you could play as much as you wanted for pretty good money. These days not so much. Less money being payed out means less money to spend on gear for many of us.
4) The "music middle class" is dwindling much like other sectors of the population. A good percentage of us can afford (or simply prefer) only cheap basses. Some of us can afford $10,000 basses. And in the middle there is less and less market every year. I would argue that for every $700 Ibanez or $800 Carvin customer, there are more than a dozen $100-$200 Squier or Dean customers. So, if you have a bass listed at $500-$1,000, even if that is a fair price, there just isn't enough market to support them used along with all the other new bases in that price range.
5) Quality at lower price points has risen at a steady pace for years. These days you can actually get a playable bass for $100-200 new. Not my preference but plenty good enough for many. So, many of the new bassists who haven't been privy to our bass snobbery will reckon "Why would I buy that guy's used Stingray for $750 when I can buy an OLP that looks just like it for a couple hundred?" And then the OLP actually plays OK to them further stamping out the mid priced used market. Cuz many of them don't care what name is on the head stock.
6) The market is flooded in general. I have a CL app on my phone set to search "bass" in the musical instruments CL sections of half a dozen neighboring areas. At any given time I can find dozens of bases and amps for sale right here within a couple hour's drive. And most of my area is rural. Add to that web sites, TB classifieds, other forum classifieds, local Bargain Hunter/Trader mags, and at any given point there are literally thousands and thousands of basses for me to choose from at any given price point. The odds of someone landing on your bass here at TB are pretty slim. Your bass for sale here has a one in a million shot at being seen by someone in the market. It's like trying to find a needle in a pile of needles.
Short version: Most of the people who want a $500-$1,500 bass (new or used) have one and don't want/need another one. There are less and less of those people every year due to both economic factors and the simple fact that there are less people (particularly as a percentage of the population) wanting to take up guitar or bass. I wouldn't buy anything unless I were planning on keeping it for a while.
In fact, due to the depressed Loonie, and therefore the raised prices of new US goods, the Canadian used market in general will take off.
