It was recently revealed that some major Switch games wont support cloud saves, including Pokemon Let’s Go. If you want to read more about that then click here.
In a comment to Game Informer, Nintendo said the following:
“The vast majority of Nintendo Switch games will support Save Data Cloud backup. However, in certain games this feature would make it possible to, for example, regain items that had been traded to other players, or revert to a higher online multiplayer ranking that had been lost. To ensure fair play, Save Data Cloud backup may not be enabled for such games. To ensure that Save Data Cloud backups cannot be used to unfairly affect online multiplayer rankings, the feature will not be enabled in Splatoon 2.”
As many people speculated, some Switch games will not support cloud saves in order to prevent cheating and “ensure fair play.”
Source: Game Informer