This is definitely something that attracts me to PuTTY. There _is_ something reassuring about applications that look the way PuTTY does - maybe the aged look projects stability due to lack of change, maybe it's just the additional cohesion from using OS primitives, I'm not sure. What I am sure of is that I find the opposite to be true for apps with a "modern" aesthetic; the more material design, rounded corners, transitions, low contrast, high padding I see, the more I experience feelings of distrust and skepticism.
I'm not qualified to psychoanalyze it, but I'd hazard that it's not an uncommon interpretation in some user groups, given the pockets of fans of PuTTY-esque design.