This might not be an issue of the web being less open, but a recent change in online socializing. This is my (completely thought on the spot) interpretation:

More users of social platforms who set their content as public, are expecting stranger visitors to simply consume their content on a superficial shallow level. Like maybe just gloss through the past few weeks or something. And then from there gain the simple impression that this user is interesting/happening/whatever positive. So it's a bit of peacocking on the Internet.

Digging deeper would sorta "violate" the social customs these users are used to. They don't really want strangers to know what they did months or years back, because only their close friends would be the relevant parties who deserve to know that, on the basis of the long time spent together. But to have to tweak the settings of each piece of content that becomes "too old/far back" is troublesome.

It's an interesting variant of the online diary. The user wants people to know his/her recent activity, but going further back breaches his/her threshold.

Probably why things like Snapchat are getting popular, where the microbursts of content have extremely limited lifetimes. It's short enough for users to simply share their latest activity, yet make it somewhat harder for strangers to trace back far enough. (I mean viewers could just quickly download the content but it's still a significant enough barrier to deter curious strangers)