Because it gives opportunity for the startup to grow and angel investors are experienced
seed comes from someone connected with the company
As Angel funding comes from wealthy individuals/firm who may alreday be market leaders and have stable market base, chances are more likely that the startup business can fetch more trust among other future investers and that the products/services may have more exposure and confidence while launched in market.
When there is a product, there is a better chance, to invest in it.
