Small seal script (小篆) is associated with Qin unification: one set of official graphs for a newly unified state. Whether every detail of that story is as neat as later histories claim, the idea stuck. Chinese writing has been standardized, then standardized again, several times.
Seal script remains a calligraphic and seal-carving style. It is not what you type in a spreadsheet. Clerical script and then regular script became the practical hands.
Modern simplification is another official standard, not a return to seal forms. When this site converts 门 and 門, both are regular-script descendants in Unicode, not 篆书.