Another webpage about the situation today of tenkara in Japan. That I found somewhat surprising. Tenkara fishing is also banned on some managed streams, (fishing spots) in Japan. Just as it is banned on some streams in the USA.
In the USA people from have reported that tenkara fishing was banned on fly fishing only streams in their states. Most often it was banned due to the local law stating a reel must be used with the fly rod on fly fishing only streams. Other states seem to not include the reel requirement.
Tenkara fishing on fly fishing only streams seems to not be a problem in states where the rules do not specify a reel must be used, or may be permitted where local officials recognize tenkara as fly fishing and do not enforce compliance with the reel rule.
I do not know if similar reasons are behind the rule requiring a rod used on fly fishing only streams in the USA must have a reel. But it maybe the same reasoning is behind the reel rule. But I have never read the reasons for the reel rule.
According to the below webpages the main reason given for banning tenkara fishing is because it is difficult to distinguish it from bait fishing. But there are also a few other reasons given for banning tenkara fishing. The Japanese have many methods of bait fishing that use reeless telescopic rods that are not widely used in the USA. Making it a bigger problem in Japan than here to tell the difference from a distance.
Why are many managed fishing spots banning tenkara?
https://himajintsurinado.com/tenkara-kinshi digital English translation
テンカラ禁止 [ Tenkara kinshi ] Tenkara prohibited (banned)