To get a 'good' job, you need to have attended the 'right' school. To get 'good' investors as an entrepreneur, you need to know the 'right' people (which is also influenced strongly by where you went to school).
To get into the 'right' school, you need to optimize for that result. If you're working full-time and trying to pay your own way, good luck. Kids that have 'helicopter' parents who have the means to support them and encourage (or force) them are already a leg up on the poorer competition.
All of these factors of course just serve to entrench the upper classes, and reduce social mobility (which, while it exists, it's very difficult to move up). Poorer students have much less time and money to do the 'right' things, and while there are always outliers, they don't determine the direction of society.
We could always build a more egalitarian society (basic income, free health care and post-secondary education), but equality doesn't always appeal to our perception of 'fairness'. And the benefits of equality (a happier, less stressful society) aren't something that we can necessarily quantify, especially when it's 'our' taxes that pay for it.
Anyhow, my point is, this trend will continue, because it's nothing more than a reaction to institutions already in place.