Angiosperms are the most successful plant group is because they have pollens and flowers/fruits. The flowers are able to attract insects and this allows better transportation of pollen. Also, animals and insects may eat the seeds, and that would also be good transportation of the seed because the seed is usually excreted.
Angiosperms also go through something called double fertilization, which helps the plant
They have a lot less cells than gymnosperm
MOst importantly they have vessels that can escalate their growth
