Every technique I have ever seen, and every movement I have ever seen, seems to be against a very committed attack. They rely on the uke putting their body and their momentum into the thing.

Yet most of the fighting I've seen has very little of that, and much more jabby movement, snap kicks, and as a general rule, people who do not commit their body to attacks. These type of things seem like they would be immune to most of the small joint manipulations that make up the bulk of the Aikido I know, (although I'm sure an experienced aikidoka could enter through them)