My quick take on why Base by Coinbase might actually be the thing!

iirc, they have their own scaled version of an orderbook for eth, allowing for txn to be onchain, but optimized to reduce gas fees, they can better compress the margin and offer a more affordable building platform. 

if yes, brilliant!

But why not just create their own chain on Cosmos?

Co-Founder & CTO https://monitor.completionhq.com/

idk. 

my guess would be that eth is a more scaled L1 with a better liquid market than cosmos, they want to be directly plugged to eth network without a middle man, or just their belief of eth network over others. all guesses from my side. 