The big difference is that Yahoo makes money. The disappointment with them is more in the vein of they coulda, woulda, shoulda been Google or whatever and they're not and never will be through various iterations of high profile execs. But with some exceptions (such as Flickr, maybe Finance), not that many would really care if Yahoo shut down next month.
Twitter, on the other hand, operates infrastructure that a lot of people care about but can't make money and seemingly has no plan for how to change that.
They did if you assumed the IRS was going to approve a tax-free spin-out of the Alibaba stake (and at the price Alibaba was trading at at the time). As it transpired the IRS did not approve such a spin-out and Alibaba's price has dropped post-IPO.
Twitter, on the other hand, operates infrastructure that a lot of people care about but can't make money and seemingly has no plan for how to change that.