I was the editor in chief at Dr. Dobb's, which many of you know closed down in December. As I explained in my farewell editorial [1], our ad sales were squeezed by a comparatively recent phenomenon in media, which is a very steep drop in vendors' willingness to buy Web ads--a lifeline for most web sites.
The reason is that vendors have (finally!) discovered that effectively nobody ever buys anything by clicking on a web ad.
For certain consumer sites, that's a survivable problem. For example, Budweiser's ads aren't intended to make a sale, but rather to remind people of the brand. However, for many tech companies (those that aren't tier 1), they don't have the funds to do brand-oriented ads. Their ads need to result in clicks and purchases. And that's just not happening on pure websites. (FB and Twitter are a wholly different category.)
Personally, I expect that more web sites in the tech sector that have depended in the past on advertising will either fail or drastically cut back on their offerings.