I mean, no one's forcing you to. That's my point though!
Casual web visitors to the public-facing (no account needed) portion of the product simply aren't exposed to the majority of the product, and have a sub-par experience as a result. This reduces the likelihood of the product being successful. Some products try to solve this with a hard login wall, but that's problematic for both casual viewers as well as a portion of the content creators. There's no good solution.
In the example of Tumblr, even if you just want to consume content without posting anything, the reading experience is much better in the logged-in dashboard (newsfeed / activity stream) vs separately visiting random blogs that all have different themes.
> As for the other side, publishing your texts or photos on the Internet for others to view, isn't enough?
If you want to just publish photos, you can use a product that specializes in this, rather than choosing a combination publishing site / social network where the community interaction is inherently a huge part of the product.
No, their experiences are perfectly fine.
Maybe the company believes that monetization is worse when account-free users read the site, but being account-free is an ideal experience for the majority of users. Companies love to lie about this, both externally and internally.
Going back to my Tumblr example, I've had a lot of conversations with people on HN who fundamentally didn't grok that there's substantially more to the product than the public-facing blog network, in part because there isn't a login wall. A few examples:
https://news.ycombinator.com/item?id=28607197 (interesting quote further downthread "I never felt the need to make an account since I was just reading. They didn't make it clear that the service was incomplete without an account.")
Meanwhile the Tumblr dashboard (logged in user experience / social network side) has a uniform user interface which does provide these things.
But there is no way for Tumblr to prevent this problem on the blog side while still allowing users to have full control over their blog's public appearance. If they forced themes to contain specific template tags or design elements, it would no longer be usable as a freeform CMS.
Same reason Tumblr doesn't/can't have a login wall. But as a result of this, casual readers get a mistaken impression of the product and its capabilities.
It's primarily a social network, but that's never clear if your only exposure to Tumblr is some random blogs, some of which use blog themes that have usability issues. Most of Tumblr's functionality is literally invisible to you if you never create an account. It's a lot closer to "LiveJournal meets Geocities" than it is to WordPress.
However, a login wall was a no-go since it's obnoxious and interferes with users who want their blog to be a public-facing presence, or use Tumblr as a CMS, or as a traditional blogging platform etc.
In terms of the "login wall or no" question, for platforms that combine social networking with public-facing user-generated content, I don't really think anyone's found a good solution yet.