Bench press vs weighted push ups?

Hey Starting Strength community!

I’m writing because I have a question in regards to why we start with bench press.

From my understanding, we begin with the main lifts for the purpose of incorporating the most muscles possible. But in the case using bench press instead of weight push ups, wouldn’t it stand to reason to use weighted push ups as you are utilizing more muscle groups?

Thanks in advance!

Discussed in the book. Read the book.

This topic was done completely to death in the forums multiple times over several years. but despite that, we still do not know how much weight was in the backpack.