Install mac OSX El Capitan on Early 2009 MacBook Pro 17" Unibody

Erase and reformat a storage device in Disk Utility on Mac - https://support.apple.com/guide/disk-utility/erase-and-reformat-a-storage-device-dskutl14079/20.0/mac/11.0

The link only has versions down to High Sierra but if you ignore anything talking about APFS I think there shouldn't be huge differences. Browse the Disk Utility documents to read about partitioning and formatting.

We can't tell you why unless you provide more information such as what you see when you try to install it.

Did you format the new drive correctly? Use Disk Utility and make sure it is partitioned to GUID and using HFS Mac extended non journaled.