The reasoning was that they wanted to keep down the amount of games (so the time frame and impact on the hosting nation isn't too large) and that no team plays more than 7 games, just like now (pressure from the clubs so their players don't get injured).
Now it's 6 games per group, so 48. Then 16 teams in the knockout stages, meaning another 16 games.
2026 it will be 16 groups with 3 matches per group, so 48 games like now. 32 proceed to the knockout stages meaning another 32 games. Also, 32 teams will get 3 matches, just like it is now.
Only 16 more games when adding 16 teams while guaranteeing that the same amount of teams are guaranteed 3 games is mathematically pretty neat, but it comes with collusion problems and that the final round drama won't be as profound.