These are great points, and looking at some of the other responses I get the sense that it’s a time and skills issue. So, what exactly do communists and socialists imagine will happen when “workers seize the means of production”?

I admit I'm not a scholar in this area, but my college reading of Marx and Engels they were taking about nation-state levels of "seizing the means of production". As in, the entire nation's ability to produce goods, grow and transport food, facilitate communications, etc. Doing so on such a grand scale that the elites/bourgeois would be forced to cede control of the levers of power because society effectively halts with the means of production in the hands of the working class (proletariat).

Marx wasn't talking about a socialist group starting up a competing grocery store to the entrenched established players in that market space.

I don’t want to discourage anyone from pursuing these ideas, I think at least in the U.S. it might be cool to have a consultancy or non-profit which helps connect such founders and provides them with education, training and startup resources.

There are educational resources for starting non-profits organizations (and I'm assuming co-ops). The real resource any org (for-profit or nonprofit) needs to start up is: large amounts of money. In for-profit ventures (assuming your business plan is respectable) you can get bank loans or outside investors. Both of these groups expect a return on the money they're giving you to get started up.

With a co-op, I'm guessing the only sources of startup capital are: government grants, philanthropic donations, or a founder that already has amassed their own fortune.

Edit oh and some of the other points are that one wouldn’t get rich doing this. So what?

At those really dark times for your business you ask yourself "why the hell am I even doing this?" for most business owners the answer is "so that at some point in the future my life will be much easier". For a co-op, there has to be a very deeply held belief that what you're doing is extremely meaningful and your sacrifice will be "worth it" somehow. While those people exist with almost a religious level of obligation to their cause or their community, I think they are extremely rare.

I don't envy the leadership in a struggling co-op. Running an organization is hard enough at the best times as a single owner. Having to run it by committee when it is crumbling sounds like a painful death.

I’ve already seen people look down on wealth accumulation, so I think it’s fair to say that the motives for someone who’d start such a business venture are different, which is valid and reasonable.

You may already have your answer. In your first post you said: "I’d also like to see more childcare co-ops, or community shared pre-k schools."

What is stopping you from you creating a child-care co-op?

Secondly, I don’t think market forces will impact such businesses because if you’re creating communities around them, then people will choose what they know and trust.

This is naive. Market forces (and other externalities) can have massive impacts on your organization irrespective if you're a for-profit or co-op. Just think of what COVID did to many organizations. Though nothing change in the business model or service offering, thousands of companies went under because the conditions of the market changed through no fault of the organization owners/leaders.