Price fixing would require every single company selling something to cooperate. And if they do, another person sick of them can start a new company and undercut them. Price fixing would also destroy any goodwill towards these companies and many customers wouldn't patronize them even if they lowered their prices again.

Yes, most of the very rich have acquired their wealth through unfair means, be it through unfair government action like intellectual property, subsidies, bailouts, low-interest loans, etc., or violence, historic or current. Regarding pure socialism/communism, a war to fully redistribute the riches of the wealthy will likely never happen, and cause great devastation if it did.

In a libertarian system, even if everyone started out equally wealthy, some would end up richer than others, as people of differening competency and diligence should. But libertarianism makes things fair even if some are very wealthy.

One who owns a lot of resources can rent or loan it to others without much additional cost to themselves, and make a percentage return. But by making them compete with other rich people, assuming resources are plenty, the ones that offers it for the lowest price, ie., makes the closest to zero profit, will get all the customers.

As for why even partial wealth redistribution isn't preferred in a libertarian society, note that the company that provides the customer with the most value for their money wins. The riches of a wealthy person are assets to be used to finance their business, even if turned into houses or jewelery, since they can be liquidated when needed. Taking these away punishes the best company, which is counter-productive. If a lot of it is turned into stuff like parties and luxury vacations, the company isn't being very efficient, and will likely be replaced quickly in a free market. If not, that means people who can afford it are willingly transferring their money by overpaying due to their affinity for the entity, in which case libertarians would argue they have every right to spend that fairly earned money.