I think that there can be a few factors in that. Compared to bar ends I find them about the same as far as ease of reaching them if not a little easier. For me they are pretty much the same height as bar ends but further back. That is at least in part because I ride a fairly small frame and have my bars pretty low. Folks with larger frames and higher bars will see more difference. The fact that I spent a lot of years using down tube shifters is a factor as well.
I have found that with bar ends I tend to bang them with my knee, again may not be an issues with a different frame or different cockpit setup. Maybe a minor annoyance, but I also found that bar ends tended to get bumped out of gear when the bike was leaned against a wall, or railing.
Well, I ride middle size frames (56 or 57 cm) but agree that downtube shifters aren't a lot less accessible than barends. However, I find both to be too "out of the way" when I need to shift in a hurry because strange terrain surprised me. You can't always anticipate the need to shift and taking your hand(s) off of the hoods isn't always easy.
I rode both friction and indexed downtube shifters for several years and tens of thousands of miles and was thrilled when something better came along. But barends, which I've used and still have on one bike, weren't it.
I used brifters, both Shimano and Campy, for many years in 7,8,9 and 10-speed form and while I loved the convenience I wasn't thrilled with the expense or perceived fragility. So, what do I do now?
In a word, "Retroshift" (now renamed Gevenalle). These mount either downtube shifters or barend shift levers right on the brake levers. All the convenience of brifters, the simplicity, low cost and durability of downtube/barends and cheap "upgrading" when you wish. I have them on three bikes and see no reason for anything else. For you friction shifting fans, they are available with friction levers both front and rear and you can mix-and-match components to your liking.
And, no, I have no relationship to Gevenalle, either personal or business. I'm just a satisfied customer.