> Furthermore, more competitions and more matches means more opportunities for more players to play a part.
In reality, coaches are under pressure to always put up an A-level selection. For the FC Bayern, that means Manuel Neuer between the goalposts no matter if the opponent is FC Chelsea or Greuther Fürth (the current bottom of the Bundesliga). The only scenarios outside of regulars being injured where coaches are fine to experiment with B/C level players are friendlies, training matches and irrelevant games (UEFA CL group phase, when the result of the last game does not matter).
> Not to mention that a World Cup every two years means much more host countries, which can be huge, for local fans and the sport locally.
Unfortunately, a World Cup requires large, expensive stadiums - billions of dollars, usually borne by the tax payers. In countries like the US or most of Europe, it is economically feasible to either use existing stadiums or build new ones (like Germany did) that get used for decades afterwards. In countries without a large (!) football fan community, these will all either rot or cause massive financial losses for their upkeep - like what happened in Brazil and South Africa [1] or Russia [2]. Qatar will likely be even worse, they already plan on one of the stadiums being torn down directly after the World Cup [3].
Not to mention the supporting infrastructure (public transport, hotels, press venues, roads) - if the stadiums aren't used to capacity, that's a lot of waste there too.
> I'd love to see more neighbouring countries host
That only spreads the expense, but the waste will be the same. A World Cup (and for that matter, also Olympic Games) only make sense in countries that can use the infrastructure at the designed scale for decades.
[1]: https://www.musikexpress.de/millionen-projekte-was-aus-den-w...
[2]: https://www.faz.net/aktuell/sport/fussball-wm/hohe-kosten-ka...
[3]: https://www.stern.de/sport/fussball/wm-2022-in-katar--neugeb...