They lose the ability to claim experimental when it has passengers (and in my opinion also since it is not doing anything particularly innovative... It is "just" a capsule). We dont risk astronauts like that. Spaceflight is risky enough as is.

And the traditional space companies (like boeing) spend so long on design and engineering and testing specifically so that things go mostly right the first time. This is now the third launch and its still having issues despite now risking crew. And that is with several years between launches. Its not a good look for boeing here if they cant get this capsule absolutely rock solid.