There's a world outside of web apps and SV tech companies. There's a
lot of big datasets out there, most of which never hit the cloud at all.
Story time: I worked on one project where a single (large) building's internal sensor data (HVAC, motion, etc. 100k sensors) would fill a 40TB array every year. They had a 20 year retention policy. So Dell would just add a new server + array every year.
I worked with another company that had 2000 oracle servers in some sort of franken-cluster config. Reports took 1 week to run and they had pricing data for their industry (they were a transaction middleman) for almost 40 years. I can't even guess the data size because nobody could figure it out.
This is not a FAANG problem. This is an everage SME to large enterprise problem. Yeah, startups don't have much data. Most companies out there aren't startups.
By the way, memory isn't the only solution. In the past 15 years, I've rarely worked on projects where everything was in memory. Disks work just fine with good database technology.