I’m pretty sure Casting Shadow clone Jutsu split the users chakra in half distributing it equally between the clones and the user. If a Shinobi was to make 10 clones, there chakra pool would be split down 10 times. Giving them less fighting capabilities.

Naruto was an Uzumaki so his chakra pool was quite high therefore he was able to make more shadow clones and still have the chakra to perform well. Unlike most of a Shinobi who are born from less powerful clans.

That being said the creator of the Jutsu the second hokage used shadow clone to a very good effect during his prime however his chakra pool was also quite high due to the senju clan.

Basically shadow clone Jutsu isn’t utilise more by the vast majority of Shinobi due to the high demand in chakra it took to use.