Edit history

You imported. This will have brought in just the latest edited state that had been written out externally, for each image file. Not only have you lost the history of prior steps in that editing, you have lost any Collections you had made, also any virtual copy versions (including proofing copies) you had made. 

The preferred method is to copy in the Catalog from your old computer and open that instead of using an entirely fresh Catalog. This transferred Catalog preserves all your previous work of importing, organising and editing images along with their full Develop history.

You may find the storage addressing of your images in the context of the new computer, differs from where the old computer had them. This is fixed by re-browsing the top level containing folder seen for these images, within the transferred Catalog's Folders panel. All those image files and their folders will then get re-connected suitably, to carry on seamlessly as before.

This does depend on the relative organisation and naming of all these image containing folders, and files, having been kept the same in the meanwhile.

You should not have done it that way, so perhaps it's an idea to start over and do it properly: 

https://www.lightroomqueen.com/how-move-lightroom-to-new-computer/