The problem is the mental overhead, not the fee. If every single article click adds an extra mental overhead of "is this worth paying for? how much have i spent this month on reading?", people will simply stop clicking. Headlines are already super optimized to get you to click. The impact of a mental tax before every click would be at least -10x a good headline and seriously puts the media company at risk of bankruptcy. A fixed fee per month is psychologically and logistically easy to manage. There may be other concerns about cost per transaction & payment networks, but they are secondary honestly.