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host nations should not be provided with automatic qualification. They need to qualify through the qualifier tournaments, just like the other teams.
While this would be the fairest option this is never going to happen, if I am not misremembering there was a time in which the world cup champion was also given an automatic qualification to the next world cup so they could defend their championship and later this rule was abolished, and in theory it would make sense for the host nation to also be forced to qualify on their own, but this is about money, and if this rule was abolished all host nations on their bid to win the rights to host the world cup will ask for automatic qualification anyway.
Yes, it is about money. In most of the cases there are so many big investments which are supposed to be done to accommodate the world cup in a nation. Stadiums, security, logistics, hotels, advertisement, etc. The many component that can lead a country to accept to take care of all those things is to watched in live their local selection to contest for the title of the world championship, otherwise it would be more difficult for politicians to spend that money if the national team is not even going to be present.
I mean, in many cases we are talking about country that suffer from serious social problems and some people may find distasteful to expend some much in an event like this one, it would be perceived even in a worse manner if their selection was not even there to play.