They rather take the risk of unproven tech if it means they need to invest less, than go with the more expensive but proven option. Keeping in mind the relatio

They rather take the risk of unproven tech if it means they need to invest less, than go with the more expensive but proven option. Keeping in mind the relationship between liquidity and risk, this shows they don't need new capacity too soon/desperately. Also keep in mind things like making delivery cheaper in city than suburbans. There's lots of small cheap (in terms of investment, if not revenue hit) ways to make things more efficient. In that case, the fact that they rather make shipping rates artificially flat for appearance's sake says something about the long-term large-scale laxity of the economy, these recent specific bottlenecks not withstanding.