I don't think Apple hopes to make significant revenue from ticket sales: this venue has seats for only 600. The purpose of the 600 seats is to give musicians optimal conditions for the creation of music (to be recorded or streamed live) and to showcase to selected audiences (e.g., journalists and other influencers) Apple's audio technologies: the venue is outfitted with a custom 48-speaker Spatial Audio sound system.

And like others are saying, it is at Battersea because Apple has about 500,000 sq ft of office space at Battersea. It's their UK headquarters.