Low volume sales. In many cases with what's being sold in the community, hand-soldered PCBs that can often take hours to assemble and test. With something like boards for JJ, Stern, etc.. it's still relatively low volume compared to consumer devices.
Quite a few people hit the nail on the head above. People want to compare their smartphones or some other gadget that was bought for $50-100 and seems to be a lot more complicated, but it really does come down to mass produced versus low volume niche products that don't sell but a few handfuls a year in many cases.
Something else not mentioned. Household income over 75k here in the US, you're kicked into the 25% Federal Tax Bracket on income over 75k. Eventually the people that don't realize they're a business, find out when they're making $1-3k/mo selling stuff it's no longer a hobby. Then they start learning how taxes affect their business and realize they've practically been giving things away after factoring in taxes. It's not just Federal Taxes.. total taxes amount to roughly 45% once you've hit 75k household income (Federal 25%, State 3%, Local 1-2%, SS/Medicare 15.3%).
So lets say you make $100 sale on something that cost $10 in materials and 2 hours of time. There was also a few dollars in Paypal fees. So let's assume $87.00 net profit there right? Well, welcome to America.. you get to hand $40.00 of that over for taxes. So now you're down to $47.00 take-home profit. Yet the item took 2 hours to build, there was testing, there was customer support. Was it sold on a marketplace like eBay/Pinside? Fees there too. Oh and 10-15 minutes packing the order, recording the sale, possibly some other shipping expenses. So at that point it's not even $23/hr actual take-home you're working for.. it's much less than that. I've worked lower than $8-10/hr actual take-home profit many years, I'm sure of it. I've had to adjust pricing over time as I've taken a closer look at actual numbers.... and I won't even talk about some sales I've ran in the past that pretty much eliminated any profit altogether once the smoke cleared.
Why do people charge $80-100/hr for service/repairs on something? Yes they have the technical skills and the customer doesn't, but there's also operating costs of the business.. overhead, driving to the person's house or spending the time to repair the item. It's someone else's time and the rate will depend on the economic conditions (taxes, cost of living, etc) in the country they're living in. High tax rates = higher costs of things. When I started doing more work myself on my house and selling things as a business, it sure put a TON of things in perspective and made me realize a lot of things are relatively cheap if you really think about it.
Even though it's really tough to not compare the value you get out of one thing versus another in life -- you have to realize there's different conditions surrounding each product, service, industry that cause the price difference. Do you get the same $40-60 in value going out for dinner at a restaurant versus spending that same $40-60 on a video game you can play again and again? No.. but they're two entirely separate things.