I guess there is a difference between expect and assume. It would be weird for me to assume that the vast majority of people care deeply about digital privacy when clearly that's not true. Its pretty reasonable for them to assume I have Instagram or whatever when the vast majority of people do.

From their perspective, they assume I already have an Instagram account and if I say I don't then they aren't really going to understand why I wouldn't want to make one. For someone who isn't well informed on issues of digital privacy, I think this is a reasonable way to behave. From their perspective, someone demanding they download and use some random app they haven't heard of for reasons about encryption they don't understand is not reasonable.

Of course it is very worthwhile trying to educate people on issues of digital privacy. If you are able to educate them, then they will see that you perpective is reasonable. However, you aren't going to change everyone's minds