Education systems are designed to train people to be workers, not to be worker-owners of co-ops. There are a lot of skills required to start a co-operative company that people just don't tend to have. There is also a lack of financing options for worker co-operatives because financial institutions tend to view them as risky (even though they are I believe more successful on average than private corporations). Most co-ops are bootstrapped with funds raised by the members themselves.
So, in short, our economy is built around a dynamic where many people have very little and are therefore essentially forced to work for those who have a lot. The precarity of those who would benefit most from being part of a co-op is largely what prevents them from being in one. This precarity is a boon to the wealthy in society, who can benefit from having people compete in the labour market. Thus, no one with the means to change the circumstances -- such that co-ops are simpler to form -- would ever want to do so as it would hurt their position.
This is one untested hypothesis I guess. An alternative is that most people don't want the stress and risk of running a business and prefer to just sell their labour in the market. If only a small percentage of people want to be business owners and managers then we will end up with the business landscape we have.
So, in short, our economy is built around a dynamic where many people have very little and are therefore essentially forced to work for those who have a lot. The precarity of those who would benefit most from being part of a co-op is largely what prevents them from being in one. This precarity is a boon to the wealthy in society, who can benefit from having people compete in the labour market. Thus, no one with the means to change the circumstances -- such that co-ops are simpler to form -- would ever want to do so as it would hurt their position.