That's because browsers should be free. They are infrastructure, just like bridges. And nobody wants a bridge troll sitting on the single bridge crossing the internet river, demanding money from everyone.
You pay for bridges with tax. Tax funded browser sounds good in theory, but I don't trust the people managing my tax money to run a tech project like Firefox. Most likely it gets handed to the lowest private sector bidder, with the stipulation that any privacy preserving — sorry, I meant criminal hiding — features be removed.
