I mean he made the empire of the hand didnt he? Or am I confusing the timeline
Simple. He couldn't for two main reasons.
1) The EotH was always stretched for resources, it was fed units by Palpatine to Thrawn to specifically explore, pacify and to a degree occupy the Unknown Regions. They ended up with a huge chunk of space(around 250 Sectors by the time Luke and Mara found them) that was in constant need of policing and protecting. As such the EotH couldn't really spare anything to send to the Galactic Civil War-it was already fighting or preparing to fight 40 odd threats at any given time.
2) Only Palpatine and Thrawn knew about the EotH, Thrawn did not trust the location or purpose of his True Mission to the Unknown Regions to anyone lightly.(Basically if he DID entrust someone with that knowledge, that person spent the rest of their life in the Unknown Regions) This was a very informed decision based on the Empire's power hungry and anti alien nature. If Thrawn had brought resources with him to help in the campaign it would have threatened the Moff's personal power further, likely driving them away from the temporary confederation he offered(since he only had a small force of their ships to work with they didn't worry about him) Also-and far more importantly-then Empire would commandeer the Forces in the Unknown Regions by command chain or attempt to by force to fight the Rebels or each other, basically dooming the EotH's main goal in the region. This might have had further repercussions with the Empire possibly even threatening the Chiss Ascendancy for it's isolationism rather than cooperating with it like the EotH did.