If a project starts having large companies relying on it, traditionally there have been 2 mechanisms to address this:
- start a company around providing enterprise support services;
- ask for the large companies to provide some resources such as a part (or all) of an employee's time to work on the project, for the parts that are more dear to that company.
If a company is unwilling to pay, either in the form of a support contract or employee's time, it should look at another solution. Not just because they are being disrespectful/annoying/distracting to the maintainers of the OSS project but also because it means they don't have a good contingency plan for when things go wrong.
For a larger business, the value of using OSS is not to save money, it's to get the right level of customization for specific needs.