Those pools have thousands to millions of individual people just like you, who chose to join a pool to reduce the variance of block rewards. That doesn't mean they have any less share of the network.
In general, if you have a community with (say) 1,000,000 people, why would you expect any individual to have more than 0.000001% of the share? That doesn't mean it isn't for the people. It just means the world is a big place. And unlike an actual oligopoly, there's nothing stopping you from striking out on your own and claiming your fair and square 0.000001% if you're happy with the odds.
Which is 47%. Add in the fourth on that list and you're >50%.
And over time the concentration of mining has increased:
* https://www.investopedia.com/investing/why-centralized-crypt...
Seems like more of an oligopoly to me as opposed to the 'for the people' kind of thing some folks talk about.