Inconsistency with variable evaluation when autoescaping is enabled

Consider the following template:

{{ (br == "<br/>") ? "true" : "false" }}
{{ (include("partial.twig") == "<br/>") ? "true" : "false" }}

With partial.twig being:

{{ br }}

Executing this template with "<br/>" as value for the br variable outputs:

true
false

In both conditions, we test that the value of the variable br is equal to "<br/>". But in the second case only, it is considered as false.

https://twigfiddle.com/zdltz2

Why is a variable considered as safe for evaluation in one case and not the other? I understand the technical reason - "in the second case what is evaluated is the result of the inclusion", I'm more interested in the philosophical reasons: why is a template inclusion considered as less safe than a variable inclusion even though a variable value is more likely to be provided at runtime (and thus to be unsafe) than a template inclusion?

Reproduce the two expressions with the provided template and twigfiddle example, then trace autoescaping and include evaluation in the implementation. No repository files or tests are named; done would require an agreed explanation of the differing safety behavior and a clearly defined follow-up change or documentation update.