I can only speak from an audio perspective, but for most american films you dont use anything you record on set. That means thousands of hours recording each and every sound, placing it into the film, and mixing it to sound good.

So factoring in the gear cost, work hours, recording studio, etc it can easily reach a few mil on sound alone.

Edit: To answer the second question, bigger production indie films have become a lot more popular post 2020. The smaller staff sizes mean each area (usually) has more creative control; resulting in better films for farrr cheaper.

They also can’t afford expensive (and not always better) production techniques, like not using on-set sound.