Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
Your Question -
"I asked if there were any advantages to OneDrive for Business over Office 365 Business Essentials, because it looks like Office 365 Business Essentials includes OneDrive for Business plus adds other features at the same price as OneDrive for Business. If that's right, why would anyone only buy OneDrive for Business when Office 365 Business Essentials is that plus more at no additional charge? Please tell me if I'm missing something."
Office365 Business Essentials is a product bundle designed for small businesses of up to 300 users. A company cannot purchase more than 300 licenses of Office365 Business Essentials. As such the bundled is offered at a discount.
One Drive for Business (OD4B) is a standalone product. It is bundled in "Office365 Business" family of plans, and it is also bundled in "Office365 Enterprise" family of plans. The OD4B standalone product does not have the 300 user restriction.
For small businesses want one OD4B, it is more cost effective to subscribe to O365 Biz Essentials than the standalone version.
However, for businesses with more than 300 users, they need to subscribe to E1 (USD8) plan to get equivalent features as Biz Essentials.
Hope that clarifies why OD4B standalone is perceived to be more expensive than O365 Biz Essentials.