Looking for exits, China-based Amazon vendors have had a good year in 2020. Roll-ups, or brand aggregators, have been flooding China’s export-oriented e-commerce market with cash to acquire sellers. To acquire Chinese businesses, venture capital firms like Markai in Silicon Valley are raising their seed rounds. The top three, which earned over $100 million each in revenue, were the most successful. Nebula Brands, a Beijing-based Amazon aggregator, announced Tuesday that it has raised more than $50 million in a Series B funding round. Asian venture fund L Catterton led the investment. The latest financing round was funded in part by...