There are a rather substantial number of examples of smart, intelligent, brilliant shows that have found LARGE audiences. To the point where saying they "tend to have" a "much harder time" seems like a pretty strange statement to make.
Nope, not really strange. Find me shows that are brilliant that can match the ratings giants like American Idol or NCIS.

A lot of the really creative, smart, and well acted shows are no longer even on network TV anymore, in at least a small part because I think they wouldn't survive there. Shows like Mad Men and Breaking Bad average about 2.5 million viewers. Before you start going off in that weird "she mentioned this, she MUST MEAN THIS OTHER THING AND HOW DARE SHE FAIL TO MENTION A, B & C as factors!!" line of argumentative posting you're currently binging on... Yes, cable audiences are going to be smaller than national broadcast networks. Yes, lots of people view online or illegal where Neilson can't factor in viewership. Yes marketing, yes, these aren't "family friendly" don't watch these shows etc etc etc. Yes yes yes.

But I don't know who would be silly enough to claim that if Mad Men were on network TV, it would have a huge audience like Big Bang Theory (which is a good show, but not a truly great one). I would say that if Mad Men were on regular TV, in its first few seasons it would definitely have been a show repeatedly on the bubble and up for possible cancelation.

Don't take my comments for more than they are or invent arguments to debate about.

I watch a lot of mediocre shows because sometimes, all you need is something to pass the time or engage you 20 minutes (hello, How I Met Your Mother!). There's nothing BAD about that or something wrong in calling a spade a spade.

Also, obviously, everything is just my opinion. You are free to think however you want, including the idea that Elementary is a good show.