I went to a very informative conference in january where some of the top officials from F1, the FIA and various other teams and branches from the motorsport world, talked about the varies challenges and regulations of motorsport.
When talking about challenges, they brought up two things. Getting teams and manufactures to fill up the grid, and getting the audience. And a paywall is the best possible way to reduce your audience!
If I'm not mistaken, independant race teams get most of their funding from sponsors. Now, if a team approached you with a sponsoring deal, then which of the following would be most beneficial to you. A race with TV and internet coverages with no paywall. Or coverage behind a paywall, which then ensures less exposure for your company.
There's no denying that a paywall reduces the size of the audience, and if you reduce the size of the audience, you remove some of the motivation that sponsors might have. And considering how difficult it already is to aquire sponsors, this is not a good thing.
In the grand scheme of things, 30-40.000 is nothing.