ActiveRecord, like much of Rails, is all about context. ActiveRecord is designed to create a domain specific language for interacting with a relational database. By Linus' reasoning, if you had a project where interacting with a relational database was a significant and pervasive part of the app, then may be worth the tradeoff of bringing in the context and assumptions of a system like ActiveRecord.

In a huge, sprawling project in which the relational database is a small portion, it may not be worth trading the power of ActiveRecord for the accompanying loss of explicitness and clarity.