I love the fact that this is seen as the problem and fault of people in the lower end of the social spectrum. So many posters refer to 'lack of aspiration' or some special characteristics that those who are less privileged apparently lack, meaning those with all the luck, opportunities and wealth deserve it. Bullsh-t!
This country is so incredibly unequal and those on top are invested in keeping it so, deliberately excluding others to maintain the status quo.
I'm from the working classes and have had various struggles throughout my life, but have managed to end up in a reasonable situation with a comfortable life and an OK job, not struggling especially, which has enabled me to send my kids to a private school at times (several school changes). I have very often observed a hierarchy between private school children and parents, many of whom can sniff out the 'bursary family' a mile away and treat them accordingly, from freezing out the parent at the school gate to the child never being invited to play dates, being excluded from games, snubbed etc. Even some teachers see fit to pass comment and make jokes about your (clearly inferior) house as seen on camera during lockdown teaching or try to diagnose the excluded child with something to blame them for their unhappiness and low self esteem caused by bullying and being left out.
I always try to encourage and nag my children to do as well as they can at school and to aim for uni etc. We also expose them to plenty of high culture because that is what we are interested in, but still the difference between them and the children of the genuinely privileged really shows in confidence levels, opportunities, just stamina to cope with life really. When you have been 'firefighting' for a lot of your life you always worry about being just a step or two from the struggle you came from, and you get very discouraged by being cold-shouldered and excluded because you don't quite fit it. This communicates itself to your kids and no matter how hard you try they still absorb some of your weariness, apathy and anxiety.
And everything is more of a struggle for those at the bottom of the social pile. Privileged people don't have to think about the sort of things the working classes have to worry about; the privileged do each other favours, educational, social and job opportunities are passed on to family members and friends etc, but most do not deign to extend even the most common courtesy, let alone do a favour or include the less privileged in anything they do. They simply don't exist, except to do their cleaning, serving, caring etc.
So it's not because of low aspirations, it's because everything at lower levels is a constant struggle and because you get the door slammed in your face every day of your life.