Nowadays people are geared towards more reasonable average levels for modern masters. This is of great importance to artists and producers who want the best quality recordings. However, even those who are proficient with Loudness Normalization are still uncertain over specifics and implementation.
For years, the overall loudness level of songs was set based on the loudest peaks in the audio. The transient peaks were reduced by so much that the music was left without much dynamic range. There is an absence of punch and musical dynamics without those strong transient impacts which is a result of drastically-reduced peak-to-average levels.
Read more about this here: https://ask.audio/articles/some-points-of-potential-confusion-regarding-modern-mastering-level-practices