You intended to scrape out those little weeds when they first appeared at the end of May. Now the flowering weeds are setting seeds.
Weeds are diligent and determined, thus seed production is amazing. An annual bluegrass plant can produce viable seed within 24 hours of pollination. Have you ever cut a Salsify, those giant “dandelions puffs”? If you do not discard the plant, its severed head filled with merely flower buds, will skip the flower stage and immediately produce a large seed puff.