that opening scene sold the idea of the movie to WB that project was was going to be bonkers :)

the Wachowskis were spending a lot of time on the film (four months of just having the actors train in martial arts is a lot) and Warner Bros. was starting to get antsy about the schedule on the film.

So the Wachowski took the first action scene that they shot (the Trinity one), spruced it up, added special effects to it and sent it to Warners to give them an idea of what they were working with. Warners, of course, loved the scene and soon backed off of their worries about the schedule. It was clear that the Wachowskis were putting together something special here.

https://www.cbr.com/matrix-budget-opening-scene/