can I move my subscription for microsoft excel to a new mac book

Depending on how you bought your subscription you may be able to move it to your new MacBook.

• For an Office 365 subscription you can go to your Office.com portal, log into your account, and deactivate the old install. Then you can download the Microsoft installer offered on their website in order to make a fresh install on your new MacBook.
• You may be able to use the Migration Assistant offered by Apple (Move your content to a new Mac - Apple Support) to migrate the older content, apps, and subscription over to your new device, though, if you purchased a subscription key (instead of purchasing your subscription threw Microsoft.com or the Apple App Store), you will most likely need the 25 digit product key associated with your subscription to reactivate it on your new device. If you lost access to this key, you will need to reach out to Microsoft directly at Microsoft Office Support.

If the above steps still didn't resolve your problem you would need to get in contact with Microsoft Support, as Office is a Microsoft, not Apple product.

I can't think of a reason why not. Is the subscription through the Apple Store? Or through Microsoft?

Your subscription is with the user, not the machine. Microsoft can give you the details on that I'm sure. More than likely there's a chat agent on their website you can use.