I don`t think underexposure is a major problem in discovering quality roguelikes, not in 2015. Over last few years that word has become quite trendy, especially among the indie scene and I`m pretty sure any gamers -old or young, no matter - considering themselves anything above "totally casual" have encountered this term and at least some games associated with it.
Those exposed who got the bug will definitely have no problem following up - all
roads links eventually lead to this site`s ultimate database, and a day or two of lurking on forums here or on bay12 will give you enough clues as to which games stand out, yielding enough material to keep you occupied for months (in case you`re unwilling to just try some at random, which I personally think is much more fun)
In my opinion bigger obstacle in getting more people to play is poor communication and lots of misconceptions regarding the genre. I first played Rogue very long time ago - thought it`s a funny little game, entertaining for a bit but ultimately a gimped RPG, and had nowhere to learn the truth about it back then. And so I avoided the genre for the next two decades...I simply didn`t know that all I always wanted the most from videogames -depth, originality, attitude, complexity, emergent gameplay and so on is just few links away.
These days coverage and information is zillion times better and more accessible of course, but I still don`t think enough is done on more popular level to explain how the standard definition (turn based, permadeath etc) -which is kind of boring and perhaps off-putting - relates to aforementioned values.
In case of Steam itself the problem might be also the fact that the tag "roguelike" lumps everything together - and so somebody who tried, say, 3089, might have trouble understanding why on Earth should he play Caves Of Qud too.