Make sure the folder you copied into the Develop Presets folder actually holds the presets and not another folder.
Do NOT check “Store Presets With Catalog.” This setting is found to the left of "Show Lightroom Presets Folder" in your Preferences menu. If you have multiple catalogs, your presets will not show up in additional ones.
Make sure that you EXTRACTED the zip file. If you merely double clicked on the folder (on a PC), you will get access to the presets, but those will NOT be extracted files and will NOT copy/paste correctly and will NOT show up in your Lightroom.