You say of the company offering a free service.
The problem is the inflexibility of the pricing. $5 per person makes sense for a team of 5–50 people to collaborate on some project or another. It does not make sense for a company offering free classes to 10,000 students.
Half a million dollars a year for what is essentially a charity service is no joke, and not likely to be something freecodecamp will ever be able to afford.
They may have been able to spend something more reasonable, like $10,000 per year, however. There were also likely options in the upgraded service that would have helped deal with the number of users as well, but again upgrading to the most basic level of service was far too expensive.