Back in the year 2002...

Internet access was widely available.

Blockbuster video was a thing in almost every town.

Netflix mail service was getting big, making huge back catalogs available.

DVD players often included S/PDIF out for surround sound, which was becoming a more common part of home theaters.

Plasma TVs were becoming far more common, dramatically improving picture quality and size versus CRTs.

HBO and other premium channels had already gone digital with set top boxes (that also often supported surround sound), and the death of analog broadcast TV was (theoretically) scheduled for 2006.

So while I probably couldn't find any single specific reason for a peak in 2002, we had a whole series of tech improvements in place that were slowly chipping away at the edges in quality and content availability.

DVD player sales were also just starting to boom; they overtook VCR sales the next year.

Honestly I wish I had put "(or maybe a new fangled DVD)" instead of "or DVD" because people seem to interpret that as "DVD wasn't good enough to have any impact on movie sales" rather than "either VHS or DVD at the time were still shit compared to the options now so does a decrease in ticket sales really guarantee a decrease in movies watched?"

DVD adoption (and later Blu-Ray) was certainly a huge factor in the gradual changes and 2002 was when people really started amassing them at home https://i.imgur.com/OHZ9H69.png. I'm sure piracy has a role as well too, but most of the deltas listed were also gradual changes which had their start prior to 2002, same as piracy. The only thing special about 2003 is it's the year the momentum changed, not that it's the year something brand new was introduced.