Why? Because it has a female lead and there is a normal romance? I think the abundance of young male characters is really the only reason for it to be a shoujo. Otherwise it's pretty much par for the course as far as isekai go.
Its an Isekai first and foremost, but it definitely has romance, although its not the typical 'everyone is in love with the main girl' reverse harem. All signs point to there only being one romantic interest so maybe it can have romance as like a secondary or even tertiary category. But above all its a typical overpowered MC Isekai.