The reason that they get shouted down is because every time they have tried to make money in other ways it has been done in shady ways. Like giving away the browsing data of their German users to Cliqz (would probably have been illegal post-GDPR) or running guerilla marketing for Mr Robot in Shield Studies (which reduces the trust from people who enabled Shield to help Mozilla with studies).

Almost nobody complains about the them taking money from Yahoo and Google for higher placement in the search engine list. And if their other revenue streams had been as transparent I think people had been fine.