The vast majority of users don't care about the underlying encryption. That's a problem, in a sense, but the core problem here is the network effect. That it's the natural behaviour of people doesn't make it not a problem.

It makes a difference that there is not an obvious comparable alternative.

The network effect works both ways: if key people in my network are convinced to switch, other people will follow.

When I think of networks of friends and family I don't think that's the case. You'll need something approaching 50%+1.

There are a few alternatives, actually. There is also Element (based on Matrix), and XMPP which use encryption based on the Signal Protocol. Both are mentioned in the article.

And yes: users are locked in, because your whole social network is expected to be on WhatsApp. 1) you need to convince others to find you on alternatives (every single person even people you just met, you have to explain what&why; also: workplace, clubs, etc. or leave them). You certainly aren't going to convince everyone 2) you will miss out on a lot: people are being invited into groups, but they can't invite you anymore to just join; people create groups on the messenger they use most often, because it is more convenient for them. In summary, if you have a active social life and grow/grew up with it you will have a lot of friction if you really want to get rid of it. That is what I would call locked in.

By the way, this whole problem of network-effect based lock-in was already solved for telephony in the old days. Why do we have to solve it again?

Because regulation is bad and therefore we have been left at the mercy of the invisible hand of the free market.

Even this recent spate of "deplatforming" events can't seem to sway (a certain subset of) the tech community towards the idea that some amount of regulation can be a good thing.

You mean regulation as in net neutrality?