The Man United v Arsenal match is important to people for the below reasons.

Firstly, the two teams are two of the biggest clubs in England. Their rivalry is one of the most intense in the Premier League. Man United or Arsenal fans will be interested in how the two teams fare in the upcoming season.

Secondly, they played the match in the United States (US). The US has a large population of Arsenal and Man United fans. ESPN broadcast the match live in the US. It is likely that many fans watched the match online or on social media. This means that a large audience saw the match. Fans will have been interested in seeing how their favourite teams performed against each other.

Finally, the match was a pre-season friendly. It was a chance for the two teams to test out their new signings. It was also a chance to get match practice ahead of the start of the Premier League season. This is important for people because it gives them a glimpse of what to expect from their favourite teams in the upcoming season.

(See further match statistics here at this outbound link to Google).