The Champions League is a name, a legacy from the past, the best teams usually come from a select group of countries with the odd exception such as PSG from Qatar...er... I mean France.
Spain, England, Germany and Italy, any top four side in these leagues are usually far stronget than 'champions' of other 'lesser' leagues. The best competition is usually involving the best teams, the best teams are more or less concentrated in these leagues
You could have an infinitely weaker competition involving just the champions, where the champions of Sweden may get far, but that would involve smaller clubs with fewer household names or star players and poorer football. Commercially it would be a disaster.