Mmh, sitting on the fence here and there is a good chance I'll be slaughtered, but I do think that a lot of it comes down to parenting. I have always believed that early parenting is the key to the type of teens and adults children will grow into. This comes with the usual disclaimer about severe disabilities/ conditions etc not featuring in this, but let's face it, those are rare - much rarer than many will care to admit as we do over-diagnose what would have been seen as personality quirks not too long ago.
The key is to raise children with a degree of resilience, and part of that is allowing failure. It is no surprise that many of the young adults we see these days lack basic grit; they were raised in the era where Labour advocated that no child must be allowed to fail at anything and we handed out certificates for participation rather than celebrating winners at the likes of sports day. I remember spending hour upon hour with students re-taking exam after exam until they passed, re-drafting coursework over and over with way too much teacher input until it was just about acceptable.
We are indeed raising a generation (now turning into a second generation) of children who have rarely ever - if at all - been allowed to experience failure, and learn from it.
Much of it is down to misunderstood love, where a child throwing a tantrum over losing a board game is avoided by letting the child win on purpose, or a child falling over is immediately over-comforted rather than accepting that all of this is part of learning.
Some of it is down to lack of time and/ or resources due to other pressures: how many children are not allowed to help in, say, the kitchen, because it would get too messy? How many do not tidy and clean their rooms, because it wouldn't be perfect at the age of 4? Sadly, those pressures - be they due to outwards pressures of perfection or simple lack of time - lead to parents doing more and more for their children, which does lead to learned helplessness.
And then there is the over-diagnosis of, and over-protectiveness with, SEND. Yes, I'm donning my hard hat here, but it is very true that we are making way too many children too dependent on help in that department rather than allowing them to figure out strategies, which will help them in later life.
I have one class where I need to project my screen with all of a yellow, blue, pink and green background to allow for every child with mild dyslexia to be able to "access" the writing on the board. I increasingly get confronted by children who, from one day to the next, "can't read" the writing of a piece of text, because it has the wrong colour background. Those who refuse to use an overlay and need everything printed out on the correct shade of orange. I may sound callous here, but my worry extends beyond my classroom - with all of this learned helplessness, how will these students cope when they reach adulthood and their bills get printed on white paper and no one is there to help them draft their application for a loan over and over again until the numbers fit?
OP, what you are experiencing is, I strongly believe, down to all of the above. I am raising my own children with very different personalities. One is - despite suffering from crippling anxiety at times due to complications during my pregnancy - a teen who is mostly self-reliant and finds ways to deal with situations. Yes, we have had many tears and emotional moments, but we are working through how to deal with them and I see progress every day. One will exploit every loophole they can in my and everyone else's rules, but the cheeky little bugger also knows boundaries and will rarely overstep them, or shows genuine remorse on the rare occasion they do.
It is very possible to raise genuinely nice children which turn into lovely adults.