If the interpretations are accurate and complete, they'll presumably have the same impact as what is being interpreted. If the interpretations are inaccurate, then your reliance on them will not be a defense. For example, suppose TOU;dr got the arbitration requirements wrong. You could not sue ycombinator then argue that you had relied on TOU;dr, thus you were not bound by the arbitration agreement in the ycombinator TOU.

Two reasons:

1. Legal contracts are supposed to be as detailed as possible so there's as little room for disagreement as possible when taken to court.

2. It's better for companies if users don't take the time to read and understand their terms, and beyond a certain length and complexity they will just scroll through and click yes.

The "good" answer for why terms of use and contracts are written more complexly is because they encode more complex information, that is less subject to varying interpretations.

Though certainly there is a 'pattern' to these that I think lawyers just fall back into that can be less understandable than needed.

If nothing else, many contracts are written in a somewhat weird frame, where one party is referred to in third person, and the other in second person. And often phrasing is so that the second person needs to recognize a claim of the third person ("you acknowledge etc etc").

In many ways, contracts are like the ultimate reversal of YAGNI. Imagine deploying code that you literally could not fix after release, and you knew that nearly all deviations from intended behavior would just kick you in the butt. Your code (and general product function) would probably get a bit weird too.

Not to get too reductive or anything, but the reasons are very similar to why people have the authority to compel public expectations based on the arrangement of atoms (e.g. you aren't allowed to stab me, etc.). Namely: those with the power to enforce those rules think it's a good idea to do so, and the public continues to support that configuration of the legal system.