I worked at Instagram during this (not at the EeE, but saw enough of it, to see that it was a mess).

I think the reason for dropping it, is more of a technical issue and user experience, rather than a 'desire' issue or company will. From my understanding, Zuck wanted this. The implementation was a mess, and folks have different expectations about messages to appear at every platform. Having messages disappear between devices/web, or having to back up encryption, keys, etc... it was just a terrible user experience. Even employees, disliked this feature.

This was not something actually asked by users, but more of a feature done in order to thwart all the types of legal issues created when folks use the platform.

At some point, I counted, there were 64 'leads', just to make this happen. Each lead, had a certain area, or surface/views, which means we are talking about hundreds of folks involved to make this happen (across fb and ig).

It was a boodongle, and it was something that users didn't ask.

Ps. I know, many here at HN really care about this, but the average user was not willing to put up with the degradation of the user experience in order to make this happen. All workarounds, require weakening E2E, which made it pointless.

Ultimately, If you want a truly E2E, you will have to use a platform specifically made for it. IG/FB are just not it.

Even Telegram, doesn't have it enabled by default, unless you specifiy it.