You're not wrong, but the reason is more fundamental: open source and open protocols do not have an economic model sufficient to finance the
immense amount of brutal work required to make products that are easy to use and appealing for the general public. FOSS and open systems will always lose (outside nerds and certain power user audiences) because closed systems have an economic model in the form of either paid SaaS, commercial licenses, advertising, or surveillance capitalism (or some mix of these things).
... or in the case of Parler perhaps paid propaganda financing from far-right wealthy financiers...? Of course political propaganda is a form of advertising so it fits under the adware / surveillanceware category.
In software, making something work in the algorithmic and technical sense is usually less than a quarter of the work. In the case of social networks and chat apps and similar stuff it's probably only a single digit percentage of the work. The vast majority of the work is in the domain of user interface, user experience, and product design.
Even worse, this is usually the type of work that programmers don't enjoy. It involves endless tweaking, endless rewrites of user interfaces to hone in on something people like or to chase trends, and the soul crushing drudgery of bug fixes and workarounds to edge cases. Because this work is not fun, people generally must be paid to do it. Because it's the majority of the work, the cost of paying people to do it dwarfs the cost of building the technical underpinnings of the product.
I used to think that the failure of decentralization was a technical problem. I wasn't totally wrong there either. There are major technical challenges around decentralization, but I've realized since then that the lack of an economic driver to finance the UI/UX aspects are the real issue. This issue is not solvable because nobody is willing to actually pay for software.