The largest crew is during "principal photography" which is when the live action scenes are filmed (i.e. involves actors on sets or location). This takes a few months for an average movie, longer for a complex shoot like the Matrix. It seem to have been four months according to the your quote. But the whole production takes a lot longer. Pre-production with storyboarding, planning, casting, set-design, costume design etc. starts a long time before filming. The Matrix was probably in pre-production for at least a year. And after principal photography we have post-production (editing, music, sound, color grading etc.). Traditionally CGI was applied in post-production, but todays blockbuster movies are basically CGI throughout with the live action scenes composited into the CGI. Post-production seem to have takes about a year for the Matrix.

In short, a lot of people work a long time on a movie on this scale. The credit roll are the names they have to mention due to contracts or union regulations, but a lot more are involved in various support functions or as sub-contractors.

And of course salary is not the only expense. You need soundstages, workshops, offices, administrative functions. Movie equipment is extremely expensive. Set building can be expensive - for Matrix Reloaded they literally built a two-mile stretch of highway in the middle of nowhere in order to film the car chase scene.

If you need on-location shoots, there is a lot of logistics involved. Transporting a large crew and equipment to some inconvenient location and establishing the necessary infrastructure.

Keep in mind that credits usually only list people that worked directly on the noticeable parts of a movie (actors, producers, graphics, audio, editing, cameras, marketing, hair/makeup, etc) but not those who work in the background to allow those people to do their work (IT, food services, electricians, janitors, truck drivers, crane operators, finance, hr, lawyers, etc).