Be honest, how old are you.
Because I would say Reeve is a household name to almost anyone over the age of 25.
I think a lot of this poll, so far, is coloured by the fact that Evans is extremely current, as he's the main character (well, sort of) in a very successful (and deservedly so) and popular film series. CW is brilliant but I don't think it does as much for Cap as it does for other characters, Tony Stark in particular. He's still good, but he doesn't add any complexity or charm to Cap.
Don't get me wrong, I think Evans is a very good Captain America, and has grown into the role, but the thing is Reeve was something special in the role of Superman from the very first moment - so much so that a lot of the success of the film was based on two things, his performance and the special effects (because if you think about if for a moment Superman the movie has one of the worst endings of all superhero films, yet is ranked among the very very best, 93% on RT - and it deserves it, if you saw that movie as a child chances are you came out feeling like you could fly).
People remember this:
https://www.youtube.com/watch?v=9Hy6S7urCZM
There are a bunch of other actors who could pull of Cap convincingly (Chris Pine leaps to mind immediately !) but Cavill has found himself on the wrong end of comparisons with Reeve - and yes, he's not as charming, but I feel like he's immensely hampered by a terrible characterisation of Superman and terrible storytelling. I think he could be an excellent Superman - but will still fall short of Reeve.
This is more than just nostalgia, because Reeve's performance continues to influence the character. Hell, why did they bother with Brandon Routh in 2006 ? Because he can almost pass himself off as Reeve.
Also, has Captain America in the comics changed or been influenced by Evans' performance ? I ask because Reeve had so much of an influence on Superman that a number of important Superman stories feature Reeve's appearance as the Man of Steel: