Ukraine already has a lot of other domestic military production and Russia has not been able to destroy it. Major Czech and German companies are even building plants in Ukraine, so they seem to have looked at the situation and decided it is possible and cost-effective to protect then (I assume by building them far from the frontline - Ukraine is a big place)

If they can do so then it means less difficulty with logistics, more of Ukraine's limited resources staying in Ukraine, and less reliance on potentially unreliable supporting countries