That's because their prices are ridiculously high. Sure, I want access to NY Times. But maybe I'll read 1-2 articles per day. Not the whole damn paper. Same for any other site.
Blendle has been offering this service for years, though I believe they recently are backing away from it. I used it for a while several years ago, but I found using small transactions frequently to be very uncomfortable (as in off-putting, not so much inconvenient).
I vaguely recall Blendle. And checking, they want ~€2 per article, which is way too much. Consider that a digital subscription to The NY Times costs $250-$500 per year.[0] That's 365 days, with numerous articles published per day. But for argument sake, divide by 5000. That's just $0.05-$0.10 per article.
It was in the range of US$0.25-0.75, when I used it, but wouldn't you expect an a la cart offering to be more expensive than a bundle? The advantage is you dont have to pay that larger full year fee.
They already track how many times you've viewed the site in order to decide when the paywall goes up. Doesn't seem like it would be that hard to track what articles you view and charge x cents / article.
I enjoy reading the WSJ Opinion section, but last time I looked at the price, it was way too high to justify based on the number of articles I read.