Why do companies with hundreds of happy customers publish only three case studies?

I've been in B2B marketing for years and this pattern shows up everywhere: the CRM is full of wins, the website shows three case studies from 2023.

It's never because the stories aren't there. It's the production line. Chase the customer, find a slot for a 45-minute call, record, transcribe, write, then wait two weeks for their side to approve a quote. Repeat per story. Most teams quietly give up after the third one.

Here's the part that fascinates me: ask a customer to fill in a written testimonial form and almost nobody does it. Get the same person talking asynchronously about their results and you can't stop them at five minutes.

Curious what has actually worked for people here. Incentives? Doing the long way (interviewing them in a lengthy meeting/visio and writing it up yourself)? Or making it stupidly easy some other way?
Or did you just accept the three case studies?