There are a few things to consider. First, BPL is over-represented by people in their 50s and above. They generally have had more time to accumulate wealth than people in their 20s. Many have budgeted for their retirement, living frugally when they were younger so they can afford to live well when they are older. While some are quite well off, most of us are not the people who buy high end designer clothes or eat at the fanciest restaurants routinely.
Secondly, for most people, backpacking is their primary hobby. What you see on here is selection bias. Hobbies tend to be expensive. For example woodworking, skiing, riding ATVs, playing music (pianos are expensive, and serious amateur musicians tend to have high end gear), dancing (lessons, $10 weekly cover charges really add up) etc. If you have disposable income and funnel most of it towards your hobby, you tend to spend a lot of money unless your hobby is something like reading or crocheting.
But let’s be realistic here. Backpacking is a sport for the privileged and generally wealthy. Most of us have white collar jobs, and are paid pretty well for the area that we live in. In contrast, a lot of people are living paycheck to paycheck. A large number of people have no savings. Generally, they are not the people on this board. For the most part, we all have decent health insurance and paid vacation. Most of us can afford to take planes or drive our cars (often one of two in our household) to our backpacking spots. We can afford the admission and camping fees. We can afford a membership to BPL.
For younger people on thru hikes, their parents generally are supporting them. If they have no student loans, it’s often because their parents helped them, and if they do, their parents are helping pay them off. It’s a rare person these days who graduates without student loans because working through college. This is why it annoys me that younger thru hikers think they don’t need to obey the rules when society handed them a thru hike on a silver platter. For the thru hikers who have been working for a while, they are also well off. Taking a month or 6 months off would be impossible for most households due to financial constraints.
Backpacking is a sport for rich people. Many of us have a lot of disposable income because we are rich. If you were lucky to be born privileged, you will likely have an easier lot in life and more money to spend. If have a decent job and live frugally when you are younger, you too can afford all sorts of expensive gear if you splurge every once in a while. For example, $20 a month for 1 year is the cost of a cuben fiber tent. I got mine as a wedding gift from about 10 really good friends who each pitched in $50.