This is hardly surprising, because by that time, they're well on their way to becoming "invisible" to men.
So, just like men, single women 28+ are more likely to want the internet to generate a pool of people that they might possibly date.
Eventually this power wanes and she'll get approached less and less. This is the time when she might actually have to do something to find a man, and this is the phenomenon we're talking about.
Young women do not "wield sickening power over men." Some number of them may get propositioned by strangers a good deal (though, I would suggest, less than you seem to believe). That's not the same thing.
And, in any case, "not getting as many propositions from strangers" does not equate to "becoming invisible to men."
And, finally, your argument, such as it is, seems to be based on the belief that younger women derive most of their romantic partners from that mass of unsolicited propositions by strangers. This isn't particularly true, and it kind of staggers me that you seem to imagine otherwise.
If women 28+ are more interested in online dating, it seems very likely that this is principally because of a decrease in the number of qualified potential mates in their extended social circle, rather than the decrease in the number of unsolicited propositions by strangers.