A uniform with shirt and tie and blazer is not masculine?
The reason you don't see that many grown women out and about with gabardine suits in weird colours and striped ties is...?
Most suits designed for women tend to be feminine, nicely shaped, nice fabric, 'professional' yet fashionable-looking, and without a tie unless ties happen to be in. They come in a huge variety of styles and you can buy and wear whatever you feel flatters you best. By contrast, school uniform for girls tends to be ugly, shapeless, often garishly coloured, and completely unlike anything worn by anyone else in society outside of convents.
You do see the school uniform shirt and tie and skirt outfits at Halloween ('naughty schoolgirl' costumes) which is yet another reason to examine the purpose of uniform, for girls as well as boys. It seems forcing girls to wear the western equivalent of the burqa has not deterred those really determined to objectify them, and girls' uniforms have taken on a life of their own. It is always a good idea to look at unintended consequences and ask if certain choices have caused issues or fly in the face of other objectives that are more important than the problems the uniform solution sets out to cure.
By this I mean the issue of objectification of girls and women, the issue of girls' confidence in advanced maths and science class, and inclusiveness helping girls understand that it is ok to like nail polish and makeup and fashion and physics, and above all but much more importantly, helping boys understand that wearing nail polish and makeup and clothes that flatter, being conventionally 'feminine' in general, doesn't mean a girl is not their equal academically and in all other ways too. It is what uniform tells boys about girls that is really dangerous.
(I flatter myself that I do actually 'get' kids. I have five of them, now aged 14 to 25, and I regularly entertain their friends. Mine have not only been to a non uniform school but also to one where they wore uniform. I know which one they preferred, which one they dressed for with care, and which one had a little problem with out of uniform day, issues related to comments by certain children about the appearance of others.)
... A uniform that is not just attractive but clearly practical 