Question

Why were weaving and embroidery not accepted forms of art until recently?

Answer 1

That is because critics and academics are rarely open to new ideas and expanding the understanding of art. Similar thing was about movies when they first started appearing, and also about comic books. There are many critics who would still not accept these, or weaving as forms of art, but it's a never-ending expanding list and soon even video games might be considered art.
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Answer 2

Embroidery and weaving were both regarded as women's work, rather than a form of art. Only after factories were established during the Industrial Revolution and textiles were mass produced, did embroidery and weaving become globally accepted as forms of art.