Because it’s all about economics.
Way back in the 80s, the Yated Ne’eman decided that they aren’t going to be the arbiters of what is and what is not tznius and decided to make a blanket prohibition on printing pictures of woman. Flash forward to the 00’s and the explosion of frum newspapers. None of them wanted to be the paper on the shelf that people will pass over for being “less frum” so they all had to accept all the ridiculous chumras of all the other papers and then add some. There are maybe 5% of readers who will consciousnessly choose a paper without woman over a paper with woman in it, but those 5% are a big market share and all the papers have to market accordingly.
However, the same 5% are also the people who will either not have Internet access, or not admit to having it. So pictures of women on the web won’t deter them from spending their money.