In case you're interested, this is the bug report that resulted in the change: https://www.w3.org/Bugs/Public/show_bug.cgi?id=19741

The final editor's response explains the reasoning: "Change removed advice recommending use of h1 elements as the utline algorithm has virtually no implementations and as a result use of h1 elements flattens document outlines for users who actually consume the heading semantics. While use of elements of the appropriate rank for the section's nesting level is backwards compatible"