I can only talk about what I have personally tested:
Cabletica, ICE, Kolbi, Claro, Moviestar all need to be called and asked to open this port.
I have to call to open many ports blocked by default for BTC or other uses like CCTV.
I also see many other posts around the world making the same complaints.
Eh, all in Costa Rica and seemingly none of them have support for English-speaking customers. This isn't a representative sample of the worldwide Internet. And by a margin so wide that it makes your statement laughable.
From my experience trying to support the use of Bittorrent (both commercially and individually) and various RPC stacks (commercial support for home workers) I can say that the "complaints" don't equal the real ISP problems. Only somewhere between 1% and 5% are the real provider-caused blocking/interference/mishandling. The remaining 95% to 99% is on the customer-caused misconfiguration or hardware/software faults.