Because that requires technical skills most laypeople don't have.

Because no one will ever do that. Even if they risk being arrested

Criminals have gone soft then, and deserve to be arrested!

All the classic mob movies have something about never talk business on the phone, always meeting in person in some dark waterfront or warehouse location. Here, they would only be required to meet in person once! If someone is too lazy even for that, well then, enjoy prison I guess

Because depending on your threat model, meeting in person may be undesirable.

The convenience and knowledge barriers are too high for most people. It's pretty straightforward for folks with tech subject matter expertise, but for most others, it's just not worth figuring out what they need to know, then getting all of the prerequisite knowledge that lets them learn that, then worrying about screwing it up, or maybe relying on someone else for basic operations, etc.

It's often tough for developers to see this for the same reason it's tough to write documentation-- reasoning about a beginner's perspective is a specific skill that takes study and practice. That's why software companies that need financially stable products hire technical writers and interface designers, and it's a place where FOSS really struggles.

For example, Mastodon's active userbase has dropped 50% since its peak during the beginning of the Musk/Twitter debacle... even for the ones brave enough to plunge in head-first, it was too much technical resistance compared to the more straightforward alternatives that they had already abandoned. I think it was a missed opportunity.

Sorry to see people dismissing this idea. It is educational to remind people of best security practice. As for actual criminals.... I would bet some of the most skilled do.... and that's why we never hear of them. As far a socializing the practice, it's like any other skill and practice like learning to sell used cars with high-pressure methods. You just have to know it's possible, then get the word out and train people. Then they'll be able to work together on it.

They could, but it doesn't stop what happened in this case - the cops infiltrated the organization, so people who had access to unencrypted communications turned them over to the police.

Survivorship Bias. The criminals that are doing this are not getting caught, so you don't hear about it.