It is the only non-vocal instrument in those contexts.Yinks, that's a wild statement about an instrument I play professionally (organ) and I'm struggling in all charity to think of any part of it that might be true.
Most organs in the world are in churches, not primarily as a solo instrument, but rather to accompany, chant, choral music and congregational singing.
It is very much compartmentalised here. You get solo performances, you get accordion orchestras, you get some folkish music usage ("Oberkrainer" which would, if anything, be Slovenian, Alpine stuff that leans a bit more towards Styrian Harmonica, and Shanty-like music). Switzerland has more of an unprejudiced connection to accordions (with a focus on their own diatonic Schwyzerörgeli with unisonoric bass for traditional music and flat-buttoned C system for general-purpose).My greatest experience of the modern accordion is as a chamber instrument, and its taught as such in a number of conservatoires, working especially well with strings. Maybe its role is more compartmentalised in Germany, I hope not though!
Street musicians playing it more often than not are of Eastern European origin. You are more likely to see a flute or violin player with orchestral playback from a recording here than a solo accordionist.