Because a lot has changed a lot faster than ever could have been anticipated in this country. The Obama midterms were clearly less partisan than they seemed at the time. as much as partisanship has caused our politics to decay, it has worked somewhat to Democrats' advantage as well. It's why I cannot fathom 2022 being anywhere near as bad for the party as 2010 and 2014 were, though it will still almost certainly be an electoral disaster.
I bet we'll be saying this same thing about Colorado electing Gardner back in 2014 soon.
Cory Gardner’s win was sandwiched between Democrats winning the Presidential races in Colorado in 2012 and 2016 by about 5 points apiece. On the surface, his win in 2014 wasn’t that impressive if you view it from that baseline since 5 points isn’t really a huge deficit to overcome.