The Beatles stopped touring because their fans screamed louder than any amplifier known to man!

There’s no arguing that The Beatles were (and still are) an immensely popular band. But, it turns out that this very popularity caused them to stop performing live. Their crowds were so enthusiastic that after a while, their music could not be heard over their screaming.

During preparations for the US tour, they traded in their usual Vox AC30 amplifiers for more powerful 100-watt amplifiers especially designed by Vox for them. However, these speakers were still struggled to complete with the noisy masses. Over time, the band grew increasingly bored with live performances and recognized that their shows were no longer about the music. So, they decided to make the August tour their last.

(Source)