Probably some, others are not happy when games come out and there's already a ton of DLC out. Others are not happy with how it's priced comparatively to the price of the full game, then sometimes there's still regional variations in price which people see as unfair.
Others are not happy when the cost of the DLC ends up costing twice as much as the game.
Why does the total cost of DLC matter? Why does the total amount of DLC matter?
Regional pricing I grant you, but I'm constantly pissed off about that because I live in Australia and we get reamed both ways for prices. It's not a DLC thing, it's a buying any good or service thing. Standard price for a game off the shelf is $100 here, and while that sort of makes sense now it was exactly the same back when the AUD was at parity with the USD.
I think people for some reason can't get over the fact that you pay a certain price for a certain amount of product. You don't get pissed off at McDonalds for their hamburgers not being bigger. That's the size you get for the price you pay, even though they could absolutely slap a bit more on there if they wanted to.
Why is a game different? You get what you pay for with a base game. If the base game isn't worth what you're paying, don't buy it. If you do buy the base game, you may have the opportunity to buy extra things if you feel that they're worth the money.
I understand the emotional response that leads people to see DLC and go "Hey!". I don't understand how people can still be pissed off after they stop and think through it. It is literally the exact same thing that happens in every other industry, and yet nobody blinks twice.
Most I suspect just don't like feeling they are missing parts of the game that they feel they've paid enough for already, greed drives this just as it does for some of the companies who create the DLC because society seems to see greed as a good and acceptable quality these days.
Welcome to capitalism. It's been around for a while now. It seems to work OK for the most part.
Companies exist to make money. It's what they do. You might as well be annoyed at flies for swarming to cow dung.
I would also suspect younger players are much more likely to embrace DLC than the older guys who remember gaming long before they days of DLC and feel like parts of the game they once got when they a bought a game are now sold as optional extras.
I rather suspect you're wrong. Adults tend to not care that much about ten bucks as long as they're getting value, because realistically that's the difference between buying lunch at a cafe and bringing a sandwich from home for one day. I didn't blink twice dropping $25 on Witcher 3 DLC, because I know I'm getting value and that is not a particularly significant amount of money when I'm dropping $2000 a month in rent, food and utilities.
Ten bucks to someone without an actual income is potentially a pretty big deal. I'd say that most of the people who don't have an income yet can still afford to have a console gaming hobby are those who live with their parents.