The reason for this is simple, because the button header IS NOT the exact product name, you can abbreviate or set custom newline breaks. This WOULD NOT be possible if the button header was EXACT product name.
This means you can have the product name as full actual name but shorten or customise the button header to keep button text short and larger than having a full product name.
Ideal for things like wine and more complexly named food dishes.
If you change the product name you also need to update the header.
New buttons will automatically take the product name.
This issue is only on CHANGING a product name.
Your example of changing Beer to Coffee is not good as you should create a new product and add it.
Chanes are you are not going to have coffee and beer in the same category anyway and would need to remove the coffee button and add the new/updated beer product to the drinks/alcohol category.