I noticed it happened a lot on MeFi when I was active there. Vast reams of text about how terrible X is, but ask what we should do about it and... crickets.
Yes, the observation's valid, but... I don't know. When the conversation keeps happening the same way, over may topics, you have to figure there's something deeper going on.
Some guesses on possible sources of the pattern for you:
1. Criticism is fast and easy compared to thinking up a solution; building the solution; trying to show a solution works; etc. Criticism has the benefit that it can be directed to any sub-part and does not have to, necessarily, take in (or understand) the whole.
2. Criticism is, generally, perceived as "socially safer" than creation. For example, it's easier to say "I don't like X or Y about something" than it is to say "I think that X or Y should be changed to A or B." Proposing the change exposes one to criticism.
3. Criticism, in many ways (thinking of many college courses here), is what folks are often trained in as compared to creation. I think an outcome is that we learn to "see" faults more than we learn to "see" solutions. To be clear, I think folks learn to create in their vocation, but outside of that, necessarily, limited sphere, folks are most often trained as critics, rather than creators.
Yes, the observation's valid, but... I don't know. When the conversation keeps happening the same way, over may topics, you have to figure there's something deeper going on.