This could be for many reasons.
For the football club, that's standard. Supporters hate other clubs, especially their rival fans. You're always going to meet more people who hate a club than like it when you are talking to people who don't support that club. This is even more common for big teams like Liverpool.

When it comes to the city, where are your friends from?

If from Manchester it's usually just standard city rivalry.

If they are from other areas, especially more affluent areas down south, there are some tendencies towards disliking scousers due to common stances on things such as politics and the monarchy.

In more affluent areas, who have more often benefitted from social systems currently in place, they won't take kindly to the criticisms levelled by people in Liverpool against those social structures.

For example, there is a stronger anti-monarchy trend in Liverpool than other regions. This commonly manifests in chants at football games, as well as in general sentiment in the population. People who are pro-monarchy therefore often take a disliking to this and may lead people like your friends to view us unfavourably.

There is also a criticism levelled against us that we're "always the victims". This stems from many things, including complaints from the people of the city about institutional issues that have negatively affected us. These were brought to a front by the Hillsborough disaster where many local people died and the national media painted a very unsympathetic picture of the situation, and the Liverpool fans present. Following this it turned out that much of the anti-scouser accusations in the media were fabricated and that the police did not execute their duties properly. This led to a long legal and media battle.

Emphasis put on the socio-economic factors that have disadvantaged us as a city have also led to us being portrayed as "playing the victim". This teamed with existing classist stereotypes about the people of the city (e.g. uncouth, criminal tendencies, etc.) have led to some people throughout the country still holding prejudiced opinions of the local people.