What’s stopping the tau from making a astartes equivalent?

Tau are stated as having hyper advanced technology, and the main thing restricting them from beating the imperium other than the difference in size of their control/influence and that they don’t have an equivalent to the Space marines. But why??? They have advanced cloaking tech, advance space travel, advanced and arguably more sophisticated technology. Is there a stated reason they can’t/wont. Create a super soldier?

(40K lore noob only on galaxy in flames and some YT videos watched so apologies if this is a no brainer or commonly asked question)