One of the biggest reasons to time-cap it is that overall...it really isn't a good use of time.
On the other hand people are far too over the top acting as if it's the most awful thing they've ever had to deal with (it's 15 minutes and in most cases the only meeting you're going to have that day). People who can't tolerate a 15 minute chat with their team tend to have a lot of issue working well with others in my experience. The "I can't spare 15 minutes" mindset tends to live with people firmly in the "all about me" world.
It can be hard to get out of the bubble of the work that you are doing.
EDIT: I totally get bad scheduling that interrupts flow time. IMO either beginning of the day, end of the day or just before lunch is the ideal time to do it for that reason. Time zones also complicate it.
People need to emphasize that the problem is the bad scheduling of the time slot rather than the 15 minutes itself. Also, it's a good idea to make skipping it periodically totally acceptable.