I was getting pissed off about this too, but then realised I'm kind of in the same boat. I think the problem is that when you're used to not earning much and generally feel grateful for your lot, and then do something to change your earnings drastically, you then find that earning a lot more doesn't actually make a lot of difference due to tax thresholds and student loans etc.
Obviously earning more is better, but it doesn't make as much difference as you'd expect unless you're suddenly on silly money. So, going from £20k to £30k is a lovely jump, and then up to £40k is even better, but beyond that it can feel like treading water unless (I'm guessing) you hit like £150k. It also doesn't help that earning more usually coincides with taking on the insane expense of childcare... Unless you're born into money and your parents buy you a house, it's a slog to get anywhere near dreams of comfort with a little bit of luxury.
Hard agree on whoever said that things are overall so much better than in, for instance, the 80s, and I think one of the big issues is people watching a lot of TV and gobbling up marketing and living in fantasyland about what they "deserve". People really don't realise how poor they are, how far beyond their means they're living, and how much they'd have to sacrifice if they wanted to reach any long-term goals.
How often did you eat out as a kid? What did your parents consider luxuries? Just compare your life with that of your parents and for most people it reveals a lot.
It's obviously a bit galling to hear people complaining about circumstances that are better than your own, but it's all about individual expectations. And I don't think anyone who does it is indirectly suggesting that those who earn less aren't working as hard. Very, very obviously, wages have only a little to do with effort, and are mostly about your sector.