I'd guess that the people you've seen have at least one of these things, probably more: 1). Are proficient with another germanic language 2). Have lots of interaction with English even if they don't speak it (lots of folks read subtitles for English media) 3). Have learned a non-germanic language and have an affinity for picking up on language 4.) Have lots of time. 5.) Their conversational skills are limited to a few shallow subjects, and much variance on these cause them to trip up. 6.) You don't see deficits (can they spell? How is their grammar outside of simple conversation? Can they read as well as speak?)

On the whole, no one should expect to have easy conversations in 60 days, regardless of language. These are always exceptions, and are most often small talk instead of including a wide variety of subjects: Simply talking about your own interests in any depth takes some dedication, but hearing about other's interests takes more.

Years isn't on the high end: I took classes. 15-18 hours a week, with a transition to speaking practice in a nursing home (while performing some basic CNA-type work). 2 years of classes. For me, this landed me technically intermediate, but it still didn't take much to get out of my depth of knowledge. This is a pretty normal course. Some folks are faster, sure: But some are slower.