How to migrate SharePoint workflows with Powershell?

Question

I am migrating subsites to a different site collection using Export-SPWeb and Import-SPWeb (basically promoting/upgrading the subsites to site collection). However, I am losing all OOTB workflows as well as SPD workflows via this means. The SPD workflows exists and can be seen via SharePoint Designer, but all associations with list/library are lost in the destination.

My ask to all SP experts here - Is there any way we can migrate the workflows via Powershell?