Periods and other punctuation marks being placed inside of quotation marks is a typographical convention. "Full stop." If you do it differently, it will stand out, and not in a good way.
If you want your writing to be published, follow the conventions and style rules of the publisher, institution or organization.
This is not about programming syntax, or "logical" rules. You are not writing code. You are not writing in languages other than English -- which have their own conventions for punctuation marks (including different quotation marks).
In a direct quotation, there are some rare cases where punctuation would go outside the quotes. One example is asking a question about a direct quote that is not a question:
Did Abraham Lincoln say, "Those who look for the bad in people will surely find it."?
"Official English department 'rules'" is not a thing, by the way. There are official anthropology department rules, official biology department rules, official Associated Press rules, official Chicago Manual of Style rules, official American Medical Association rules, official Modern Language Association rules, and on and on. Point being, there are STYLE GUIDES for this stuff, and just as a programmer needs to know C# syntax, or Python syntax, you need to know that there are publication styles guides that spell out the "syntax rules" -- and you should know about and consult at least one of them.