Brifters are all well and good for medium to longer rides, but by virtue of putting your hands in one comfortable position they allow you to forget to move your hands around, with the result that your hands (and therefore also arms, shoulders, and neck) get sore sooner than they would on a less comfortable setup. If you have to constantly move your hands around between the brakes and the shifters, you will postpone that soreness considerably.

Aside from that, the general fatigue that starts to set in somewhere between the 100 and 200 km milestones takes a particular toll on fingers. There comes a time on a long ride when shifting the brifters is just too painful, and you don't bother any more. Since downtube and bar end shifters use a much larger (and stronger) muscle group, they don't have that problem.

I like Suntour Command shifters, as mentioned in another thread, but they have the same disadvantages as brifters in this regard.