The biggest missing factor in most beginner and intermediate players is the lack of material they are able to perform when called upon to do so. Saying that they like to “jam” is often a red flag. Not having any songs they can actually perform is a major issue. The person is really saying that “I’m too lazy to work out actual material and lack the responsibility to lead a band and deliver the goods.” The more songs a harmonica player can pull off, the more they can consider themselves a true entertainer. Songs like Happy Birthday, Christmas songs, Americana, and folk songs are all very good to be acquainted with as a player. The more songs you have, the longer you can entertain. There’s incredible satisfaction in connecting with other people through music. Learning as many songs, riffs, licks, and study pieces as possible helps create mastery over the instrument. I’m A Man, Mannish Boy, Boogaloo, Hambone, Boogie, Box Shuffle, Tramp and Cha Cha Cha all have recognizable riffs to be acquainted with that are not that difficult. You never know when you might be called upon to sit in with a band and need to play one of these well known blues riffs or grooves. You don’t even need to know the actual single note melody, but it is very important to be able to describe a groove and play it with some solid rhythmic chordal accompaniment.
My problem has been that I’ve learned songs but nobody knows them! So I end up playing stuff that I like but not that interested in. For example I’ve learned Bullmoose Jackson’s “My big Ten inch” Cleanhead Vinson’s "they call me Mr Cleanhead and Kidney stew, a bunch of stuff by Louie Jordan ( learning all the Sax solos too) and lots of different West Coast style stuff fab Thunderbirds, Little Charlie and the Night cats. But I’m always ending up playing British Blues because that’s what most people play around here. It ends up being very frustrating. They also think Blues should be very distorted and loud again very frustrating. I’d love to show people what I can actually do but I never really get the chance.
Some time ago (years ago, to be more exact) I had the same problem as @Andy2 describes in the pevious message. It occurred when I moved back to Germany after spending about 10 years in the SE USA. No one here knew any of the voluminous material I had practiced so long and hard to play well and they seemed to be unable to play any sort of reasonable accompaniment for me. It was quite depressing and actually resulted in me putting the harmonica away and concentrating more on the flute.
Now I am trying to re-learn at least some of that previous repertoire on the harmonica, but at the same time learning new harp and flute material – very slow and tedious, especially at my now more advanced age … 
That’s actually what caused me to pack it in as well. I got so fed up of being asked to play Cream, early Fleetwood Mac or just out and out heavy rock on Harmonica!!!?? Now you can actually compete with Wilde tuned harps etc better amps and so on but I really would prefer not to play, than play music I have no interest in.