Flew from MAD-MIA 28/10/2024. Ten hour flight. Attendants are fine serving food, and making sure that everyone is sitting in their seats as takeoff is delayed, important as the aircraft can't take off if people are needing the bathroom after a 2 hour delay. First hour they serve a meal which was fine. After meal service, trash accumulated, they disappeared. Eight hours later, they drop off the little sandwiches before landing. In between, they are in their galley for 8 hours, not bothering to pick up trash maybe every two hours, is that so much to ask? By the last few hours of flight, the plane is a biohazard, several of the bathrooms are cordoned off, presumably because people are dropping their trash in the toilets. When I spoke to a flight attendant about it and told them there wouldn't be such a problem if they picked up some trash a few times during the flight, I was met with a scoff that it was not their problem. Absolutely disgusting! Never again.